With BIOS, don't upgrade/update/flash unless you have a problem. Upgrade/Update/Flash all mean the same thing. BIOS flashes are completey free, offered by the motherboard's manufacturer. In the BIOS, there will be a menu where you can overclock. They go by various names: Cell Menu, Soft Menu, Enthusiast Settings, etc... Check in your manual.
What I was saying in my last post was that you should never update a BIOS that is overclocked. Bring it back to stock, update, and try your OC again. You may even get a higher OC this time, due to #1. But sometimes OC options change and the old settings don't carry on very well. Thus, it is is better to leave it at stock, flash, and then OC.
There are numerous guides to OC'ing, but if this is a C2D system, Wusy's guide is top.