After Battery change, Key doesn't needs any reprogramming. You have to resolder the new battery using its 2 connecting points but first you have to open the Key FOB to reveal its circuit. Its casing is tightly glued so it may be required to break the casing. See Youtube Video:
https://www.youtube.com/watch?v=RM6SzJ3e4uE
If your key is tightly packed then keep a spare casing handy so that you can use that to put your old circuit after battery change.