|Watch the screen as soon as the computer is started to see if there is anything on the screen about Setup. Often it suggests the appropriate key. Setup is BIOS.|
Once you get into BIOS it will show what keys are required the move around the various sections and items, also how to change things. As often as not it is arrow keys, page up/down keys and Enter key.
If you change anything by mistake look for the option "Exit without Saving" then reboot and have another go.
Always pop back and let us know the outcome - thanks