Locally -

Using the BIOS key (listed per manufacturer below) it is best to SPAM the key immediately after booting the system while the system is performing POST. The splash screen will often show that the appropriate key to use and should echoe what is listed above. I always use the alternating method between F2 and DEL since it should cover all possibilities and it rarely fails.

NOTE:

PLEASE use a standard keyboard when attempting this. A plain full size (104 key) USB keyboard will prevent a lot of issues.

e.g. Wireless connection issues, drivers not loading in time, or improper  key mapping will cause you to pull hair out before ever reaching BIOS.

Remotely -

The general idea is to access BIOS via an KVM connection. SuperMicro is a great example, if you can access the system in question via their remote management solution IPMI, a KVM session can be started. Once connected to the machine, you should be able to reset it and by using a digital keyboard the appropriate key can be pressed.

ASRock -

ASUS -

SuperMicro -

Tyan -