How to access your BIOS varies with motherboard. And WARNING: messing with BIOS can be lethal, be very careful with what you do. I've added an image of how it's done, courtesy to Link Removed
Your key to the BIOS is most probably shown in your POST, that is the white letters on a black background when your computer starts. It all goes very fast, but you can usually stop it by pressing the Pause button. The key to enter BIOS should be down left. If you can find it, it should work by pressing Esc, which restarts the process, then press the right key. It may take a bit of training, it all goes very fast. And, in case your startup is set to only show the manufacturer's Logo --- nasty bit.
Any further advice requires the make of your...