It depends on whether you have a self built/custom built or a Dell, HP, Gateway, etc. When the PC first starts and shows a logo screen (way before Windows starts), you should see something that tells you to enter Setup press some key like Delete, F1, F2, F3 or some other key. Setup means going into the BIOS. Your manual should say.
That said, if you have to ask how to get into the BIOS, it's a safe bet you haven't done so already to disable or do anything to your onboard graphics. Just the same, you can enter the BIOS to confirm is it enabled. Keep in mind while in the BIOS you only use the keyboard, not the mouse. If you do make any changes and be careful about what changes you make, be sure to save them when exiting the BIOS. If in doubt about anything in the BIOS, you can exit without saving if you want.