How can i fix the dull paint work on one side of my car to match the rest of the car.?

I recently bought a Mondeo, i got it really cheap because it had a few bodywork issues (nothing major)--one of the back doors is a different colour red and not as glossy as the rest of the car, its obviously had some work done on it but not matched the rest of the colour, it stands out quite a bit, so i was looking for some help in any way that it can be fixed either by a mechanic or myself, but none of the rubbish stuff that makes it worse, maybe a varnish and spray. any ideas.