Installation, service and repair of any HVAC Equipment should only be performed by a licensed HVAC Contractor.
A contractor can make sure you have the right size equipment for your needs. If your HVAC Unit is too small, it won't perform as you desire, and you'll be uncomfortable. If it is sized too large, it will waste energy and probably experience frequent on/off cycling, which places unneccesary wear and tear on the equipment contributing to premature failure.
We suggest you check your local Yellow Pages for an HVAC Contractor near you.