Unscrew the motherboard and remove every socketed chip, then you can soak it in normal-hot water with soap, get a stiff and soft brush and clean it in water. Let it dry for a couple of days or use hair dryer (be careful they can produce very hot air!). Hardware looks like new this way.
If there is green stuff around the battery area you need to neutralize it, there are various thoughs how to do it. Some people suggest using water combined with baking soda where the green stuff is but I have read other solutions, look up "how to clean car battery" for more inspiration reading about that.