You will have to take it to a shop that can do this service for you. You must be certified in order to obtain and work on a vehicle's a/c system.
The other thing is that if you need to have it re-charged, then there is probably a leak somewhere, since this is a closed system. That will also have to be taken care of as well.
Find an ASE certified shop or dealership to have this work done.
〉 Answered on Jun 3rd, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines