Try 4 tablespoons of salt mixed with 4 cups of water and rub on the paste. Let sit for a few minutes and then wipe off. Do not use any product with ammonia in it to clean copper.
The green patina that forms on copper is something that some people actually want. It's a matter of taste.
OMG! You DON’T!!! Leave the copper alone. The more patina they become the better. People pay tons of money for aged copper.