https://www.youtube.com/watch?v=ZBAN...e_gdata_player
That code is the master code and can't be changed. So once you retrieve it, you can set up another code that is easier for you to remember. Instructions to do that can be found in your manual.
Fob batteries can be easily changed. The fob opens in half and the battery is there. Just go to any auto store and they'll most likely change the battery for you if you purchase one from them.