Note: There is a name change going on in the industry  BIOS (Basic Input Output System) is being changed to UEFI (Unified Extensible Firmware Interface) and the older system is being renamed Legacy.  Both BIOS and UEFI are the first thing loaded at startup.  They help the hardware and software communicate particularly before the hard disk has been read. UEFI has a number of security and other advantages over BIOS.  Some systems use both.  Macs have only used UEF for some time.  PCs just began supporting UEFIs with Windows 8 but machines made as early as 2012 have the capability.  Over time, BIOS will die out.

As a side note, If the only thing you want to do is change the boot sequence, than on most newer computers, perhaps made after abut 2010, you can go "directly" to a place in the computer to boot from on the next starup.  The one caviate is that some computers such as my Dell has a differnt way of doing it so first google your computer and see how others say to do it. (On my Dell the trick is to keep tapping the F12 key while it is starting up).

If you go into the UEFI to change the boot sequnece on a computer with a boot manger, you will just see under Boot that the computer has a boot manager.

To make a one time change the boot sequnce, put a bootable USB drive in your computer then Start then the power button then while holding the shift key down, click on "Restart"
When it restarts you will see a menu, Select "Troubleshoot" Click on "Use a device" and select USB or DVD.

If this does not work, it is probably becasue you machine is too old to support this so go into the UEFI (BIOS) settings to change it.

Thee are a number of ways to edit the BIOS (UEFI) settings. 

Newer computers using the UEFI system often boot so fast that the above method does not work.  To get to the UEFI settings on windows 10 computers, click the start icon in the lower left of your screen then selecting "Settings", the gear icon. In "Settings" select "Update & recovery" (It is the last item in the menu)..  Now select "Recovery" about half way down on the left menu.  Now select "Advanced startup in the right menu at  the bottom" then "Restart Now" and the computer will start back up with a bunch of options and titled "Choose and Option.  If the second option is "Use a deivice" then select this to speicify what device, ie DVD of USB drive, if "use a device" is not an opton then you have a computer that has a speical key to press during start up so Google your computer make and model to see what it is. It will be sometning line the "F2" key.

 rs, click HERE.

The classic way was to make the appropriate key stroke during the initial stating (booting up) of the computer, before any windows type stuff appears on the screen.  To get into the setup spot, tap on the appropriate key for your machine every second or so beginning when you first turn the computer on.  It appears that for more modern, computers, perhaps 2004 and later, you need to get the key strokes in very quickly. On my new machine I tap the key as fast as I can starting just before I turn the computer on. 

What key strokes required to edit BIOS for many brands   But try DEL, F2, F8, F10 or ESC first during boot up (start up).  You may want to Google your computer to see what the key stroke is to get to the BIOS (UEFI) settings. Once you are into boot setup utility, look for "Boot" along the top menu bar.  Your computer may also show what key you need to press on an initial startup screen.  Also you can edit the settings for UEFI system from within windows but I have not done this.

There are a couple of things you may want to change in the BIOS settings.  There are a number of companies that supply BIOS software and their menus work somewhat differently and there are some differences with different models within one brand.

On all the systems you move around using the arrows on the keyboard.  IF you want to exit from a spot and the required action is not obvious, use the "Esc" key. On the legacy systems, the mouse never works because the software to run the mouse has not been loaded yet.  On the UEFI systems the mouse is supported.

A fairly good video that takes you from downlaoding a fresh verson of windows to installing it, see https://www.youtube.com/watch?v=-eDX7f6EcLA

Change the Boot Sequence

This is typically required when you want to boot from a DVD or USWB drive and you find that it is not working.  Booting is loading the first software as the computer starts up.  Computers are typically set up so they first look to the hard disk for information to boot from, then if they can not find it there, to look elsewhere such as the DVD drive or USB drive.  This makes for a faster boot.  The problem comes when you want to boot from something else, typically to install a new operating system or run some sort of specialized check such as anti-virus or hard disk check.

For at least some of the setup screens supplied by American Megatrends with windows 8 era computers, use the left/right arrows to select "Boot" from the top menu then the up/down arrows to select boot option you want to be first then hit "Enter" and do what the screen says to do next.  The option labeled "Windows Boot Manager" is apparently referring to the had disk. If you want to boot from a USB drive or stick, have it inserted before you turn the computer on or the option may not appear.

For some earlier American Megatrends BIOS's it is under "Standard CMOS Features".

Note, sometimes you will have to change it back specifically putting the hard drive in first.  It is best to do a test before assuming the system will just go to the hard drive if there is not a bootable disk in the CD drive.  You would think this would be obvious but my computer is not that smart.

Also there is some sort of bug in some Dell computers where you change the boot sequence but it is ignored.  There is a comment to the right of the boot sequence that says "A device enclosed in parentheses has been disabled in the corresponding type menu"  A Google search of the problem just showed that others were having the same problem.

Check for the amount of memory
On American Megatrends it is under "Main"

UEFI unique information
IF your computer will not boot to windows at all, you can get to the UEFI settings by forcing the computer to shutdown by holding down the start button on 3 or 4 startups and it will get you to Advance Boot Options. These options are:
Recovery > See Advanced repair options
       Use a device USB drive, network connection, or windows recovery DVD
       Troubleshoot (restart your PC with advanced troubleshooting options)
       Reset this PC (Lets you choose to keep or remove your files and then reinstalls
       windows)
      Recovery Manager (HP backup and recovery or contact HP support)
              System Recovery (Restore your computer to its original factory configuration)
              losing all your files.
              Run computer checkup (of hardware, takes many hours)
              File Backup (backup your personal data) This is a precaution, not a fix for
              current problems. Show contact information (for HP support)
      Advanced options
             System restore (Use a restore point recorded on your PC to restore windows)
             System Image Recovery (Recover windows using a specific system image file)
             Startup Repair (fix problems that prevent windows from loading)
             Command Prompt
             UEFI Firmware settings (This is what used to be called BIOS settings)
             Startup Settings
            See more recovery options
                   Go back to a previous build
      If you do a few more forced restarts you get:
     “Preparing Automatic Repair” then sais “Diagnosing your PC” then
      Restart
      Advanced options (which is the advanced option list on the original list)