You cannot change BIOS settings from the command prompt. To access the BIOS settings, you need to press a hotkey during system boot. This is typically F1, F12, DEL or INS, but may differ on your system. The key you need to press usually briefly appears in a description during boot; if not, try (keep) pressing TAB to see more information as your computer is starting up.
Note that accessing the BIOS occurs before Windows (or whichever O/S or boot device is specified) starts, so if you see your operating system booting, you haven't pressed the key quickly enough.
Most systems even have a dedicated key to choose the boot device. On my system, it is F12. Once pressed, you will be asked which device to boot from -- it does not change any settings, it just boots from the specified device that single time. On my home PC, the button is F8, but make sure you don't press it while Windows starts or you will get the screen to boot into Windows' safe mode.
Take note that not all motherboards support booting from Flash disks. There are solutions for this: you can modify your flash disk to appear as a removable disk drive, but you shouldn't do this unless strictly necessary.
Also beware that installing from a USB stick is significantly slower than from CD/DVD.