If I have a 2 ton central a/c and I want to convert it to a 3 ton, what parts do I need to change out, if it's even possible?

I know I've had bigger units put in until I finally found one that really does the job but if I were you, I would look for a good A/C person to come out and check out everything. I'm about ready to buy a new and a little bigger unit and the guy I know just said he could change the unit without having to do anything else. Best to get a Pro's opinion first.