if your current bios shows 2.48 then you are already on the current version, and there is no need to reflash the bios.
you can now power off, pull the pwr cord and press the pwr button for 10 sec and then install the new cpu, and power back on
all should be fine, if you have a no boot replace cpu and confirm new cpu is correct version (v3 or v4) and a known good cpu
the xeon1680 cpu may require a upgraded heatsink, check the hp specs to see if this is the case before installing the 1680