Turn off power to the HVAC system at the breaker
Remove the thermostat cover
Take a photo of the existing wiring
Label each wire by terminal
Disconnect the wires from the old thermostat
Remove the old thermostat base from the wall
Check the wall for damage or holes
Mount the new thermostat base level on the wall
Pull the wires through the opening
Connect each wire to the matching terminal on the new thermostat
Attach the thermostat display or faceplate
Install batteries if required
Restore power to the HVAC system
Set the thermostat to the correct system type and settings
Test heating and cooling operation
Secure the cover and clean up the work area