1- Why do you want update the BIOS? Usually you do that when you have stability problems or want install a new CPU that need the BIOS update.
2- Go to the EVGA's web page, there you can find the latest BIOS version available.
I don't think that you can change the multiplier of that CPU, maybe you are changing the reference clock that you say is 200MHz. When you change that, the DRAM frequency also change, so, you need keep the RAM the most near possible to the stock speed.