If the system needs to be recharged it may nave a leak which should be found and repaired, Most automotive parts stores sell a refrigerant in a can with a pressure gauge and hose attached. You attach the hose to the low pressure side of the A/C system. On the side of the can are instructions and normally a link to a website. Also look on YouTube look for "recharge air conditioning system" look at several video clips some good information on each even if it is not vehicle specific to your car! To carry out proper permanent repairs to the air conditioning system or replace air conditioning components requires specialized training, proper information, gauges and evacuation and refrigerant storage and leak detection equipment.