You can't treat this. This has already presented with serious symptoms that should have triggered a vet visit. If it's become pneumonia, you need a vet NOW.
The treatment varies depending on the severity of the disease. Often nebulizing the cat will help break up secretions in the lungs. Antibiotics will likely be necessary.
First off, you take your cat to a vet. He will listen to her lungs and determine if she indeed has pneumonia. He may give her an injection of antibiotics. Then he will probably give you some pills for you to give to your cat for 7 to 10 days.
treating a cat is very touchy the first thing you need to do is take it to the vet so you are sure that is actually what's wrong with it then they will be able to tell you proper treatment and procedure from there.
