AMI firmware:
F2 BIOS Settings
F7 Boot Menu
coreboot firmware:
The key to press will be displayed on screen.
Please note: If you have function lock enabled, you will also need to press the Fn key. For example, for the boot menu, press Fn and F7
Please note: coreboot doesn't have it's own interface, just a boot menu. If you're looking for configuration options, they can be changed with coreboot-configurator.