What hardware will now be running at lower voltage? I am very skeptical that a BIOS flash can make your existing hardware all run at lower voltages (which it was previously incapable of) and therefore offer some type of performance benefit. The idea doesn't make sense to me.
I have seen a lot of posts on OCN that start off with "My motherboard was working fine with no problems and a good overclock, and then I decided to flash to the latest version for (insert reason here). Now, i've been having (insert terrible problem here) problems."
BIOS flashing is different than updating your drivers. There is quite a bit of risk involved, and fixing and problems that might occur can be very tedious (unless your brick your motherboard, then your just SOL).
In my humble opinion, I don't think anyone should upgrade their BIOS unless they are having problems with their motherboard or the BIOS flash has a proven significant performance advantage.
If you still decide you want to go ahead with this, there will be detailed directions in your motherboards manual.