That's the problem with pre-built systems. They lock down the BIOS so as to limit what changes you can make. Typically, this is done so that the company doesn't have to deal with warranty issues coming from people who do not know what they are doing.
Your best bet (and honestly, I don't recommend this) is to try and find a custom BIOS for your PC/Motherboard. I would note that any incompatibilities may brick your system, making it unusable
What, exactly, are you trying to accomplish?
-Wolf sends