How to replace the air conditioning seals?

It involves evacuating the refrigerant out of the system, and you'll have to open up the system, which also means that the receiver-drier (on a Thermal Expansion Valve system) or accumulator (on a Fixed Orifice Tube system) will need to be replaced.

Legally, you cannot do this on your own. An ASE certified tech in an EPA certified shop with the equipment to evacuate, store, and recycle refrigerant must do this in order to ensure both that it's done correctly and that refrigerant isn't released into the atmosphere.