A/c- heater issues
 

My 2003 Trailblazer, is blowing heated air from the upper vents only, it will not switch to the floor vents.
Now when running the A/C the fan will not shut off even after turning the engine off and removing the key.
Also A/C suddenly will not blow cooled air.
I replaced an actuator door control about a year ago.

My heater is blowing cold air and I have been told that my blend door actuator is not allowing heat to come in to the cab.How do I replace it a