if you have the windows 8 running you can got to the start screen, select the settings charm (mouse to the right side of screen), select the advanced pc setings (bottom right)
in the pc settings, select general, then advanced startup and hit restart now.
I think there was a setting change the start up settings to give you more time to get into the BIOS.
edit: I just looked at the it. there are options to change how windows boots, debug, boot logging, vga only things like that. they don't exactly help you directly but when you reboot you should have a longer time period to get into your BIOS using your function key.
you could also try turning off fast startup in control panel. Otherwise, just keep hitting your BIOS function key until you get in. (very short time window to get it to work on some laptops)
JohnBL is correct, but the devil is in the detail. I don't remember the exact navigation, but read it carefully as you may have to experiment in the navigation a little bit to get it to work and be sure to press the F2 key with each attempt. It took me about four tries.