It varies, depending on which system you have. Usually, the maker calls the
BIOS either System Setup or Setup. When you first power on your system,
either on the maker's logo screen or on the screen that follows, it says
something like: Press F1 to enter Setup. If your system came with a manual
there should be a mention of which key to press to enter System Setup
(BIOS). If your system didn't come with a manual, go to the maker's web
site, click the support link, and get the information there.