If you're referring to how do you backup your old BIOS...
Most vendor BIOS flashes provide you the option of backing your old BIOS up before you actually flash to the newer version. Make doubly sure this is a provided option by the BIOS vendor. If it isn't, I would strongly recommend not flashing the BIOS at all...just in case the upgrade causes incompatibilities.
Another thing to keep in mind...
If the system board, with all of its attached hardware, is functioning properly...then there really is no need to update the BIOS at all. It should only be done as a last resort to solve incompatibilities with on board or external hardware.