No, you do not need to remap your ECU
This doesn't have anything to do with your air fuel ration and ignition timing. You are simply changing the gear ratio for your final drive.
Making the sprocket larger will make all of your gears a bit shorter and reduce your top end speed.
I typically do this on most of my motorcycles as it makes for better city driving. As well, a couple of my bikes have a first gear that is over 80mph at redline. It will make your bike feel a bit more responsive and help you with acceleration a bit.
Always change chain and sprockets in pairs, they wear in together even if you cannot visually perceive it. If you change out just your rear sprocket on a chain with a thousand plus miles on it, you can expect to wear your chain and sprockets at a very accelerated rate. If you change everything together you will get good wear and life out of the overall set.