When you install a new PSU, do you have to reintstall your whole computer, or can you just remove an existing power supply, add a new one, and be good to go?
yes, just have to remove the old PSU and install your new PSU no need to do anything else. word to the wise, be sure that you connect everything, and make sure all connections are in snugly
you shouldn't have to update your BIOS at all, that would only need to be adjusted if, say, you were overclocking maybe. otherwise, for a standard computer, no mods or overclocking, you should just swap them