There's probably a flash utility included in the larger BIOS files, when you unpack the file (self extracting zip file) there should be a .ROM file which is 256kB.
Most of the time it's best to use the latest BIOS update as they include all previous fixes (even if they're not mentioned for that particular update), but the latest is not always the greatest, it's kinda like windows, sometimes they've fixed some bugs and put in some new ones.
I would just try the latest first, and if it's giving you problems roll back to the previous update...etc till everything is fine.
Make sure the PCB version matches!!!