The system must first be discharged using the appropriate recycling equipment (refer the the Precautions). Follow the instructions provided with the recycling equipment as it varies from each manufacturer. It is advisable to have the system discharged and evacuated by a professional; the mechanical work can then be performed by yourself.
Air conditioning charging kits can be purchased at most automotive parts stores. Follow the instructions provided in the kit as they vary by manufacturer. Look for the A/C charging label under the hood of your vehicle. It will give the refrigerant capacity for your vehicle; do not exceed this amount!