You definitely won’t need to reinstall windows. You may want to flash your BIOS before the upgrade to make sure that the CPU is automatically detected, thus making the upgrade as simple as possible.
Should be painless. The only things you will have to mess with is the cpu and heatsink. Everything else should be automatically detected in your bios…you probably don’t need to update your bios unless the new cpu isn’t automatically detected.
Make sure you get good contact with your heatsink and cpu. I would suggest getting a new heatsink and using some heat compound like Arctic Silver to put between the heatsink and cpu.