Changing the boot order of the "bootable" devices on your computer like your hard drive, floppy drive, optical drive, etc. is very easy. The BIOS setup utility is where you change boot order settings.
Turn on or restart your computer and watch for a message during the POST about a particular key, usually Del or F2, that you'll need to press to ...enter SETUP. Press this key as soon as you see the message.
Don't see the SETUP message or can't press the key fast enough? See my How To Access the BIOS Setup Utility guide for lots of tips and tricks for getting into BIOS.
Note: The boot order is a BIOS setting so it's operating system independent. In other words, it doesn't matter if you have Windows 7, Windows Vista, Windows XP, Linux, or any other PC operating system on your hard drive or other bootable device, these boot sequence change instructions will still apply.