How do I do that?

OK you've all seen the $69.95 A/C tune up specials. What they don't tell you is you can do 90% of that for nothing. Take out the filter (you should do this once a month anyhow)Either clean it or replace it. Lay down on the floor and look up where the filter was, these are the cooling coils Vacuum them if you can. If the coils are moist from condensation turn it off and go get an Ice cream. When you come back try again get up in there with a brush if you can. No sharp objects! Now head outside to the outside unit and clear all the junk and debris away from it. Also check out the copper lines running between the systems. One should be insulated and if there are missing patches redo it. About the only thing that an A/C repairman will do that you can't is check and recharge the refrigerent if that is necessary.