AC Unit Blow Warm Air Indoor But Colder Air Outdoor
Because of the need to capture the refrigerant and licenses to get the refrigerant in most places, this typically isn't a DIY job. The fact that the outside unit is running and air is blowing inside suggests that it's not a problem with the thermostat. Check the breaker, air filters, and any other easy to access components for obvious problems. Beyond that, there are a lot of possible issues:


Compressor has failed
No refrigerant or not enough
Controller has failed or wiring has become disconnected
Inside coils have frozen over


Since the first two are the most likely and either will need a professional to repair, you may as well get one out to diagnose the problem for you.