|It will probably be F1, F2 or DEL key.|
When booting up usually an early screen will show which key to press to enter setup.
If you don't get this or it is obscured by an OEM splashscreen you can usually get behind this by hitting Esc. Or simply try tapping the F1, F2 and DEL keys while booting until one of them gets you to the setup screen.
Goin' Fishin' (Some day)