To do the job correctly, locate and fix any leaks first.

1. Recovery the old refrigerant (This will require a recovery machine).
2. Repair any leaks.
3. Evacuate the system (This will require a VACUUM PUMP).
4. Recharge the system to the specified weight of refrigerant required for your X. (This will require a manifold gauge set, and an accurate scale to weight the refrigerant).

If you want to do it on the cheap, see this guy post.

http://www.xoutpost.com/1037841-post21.html

Hope this help.