Turn off power to the HVAC system at the breaker
Remove the old thermostat cover
Take a photo of the existing wiring
Label each wire by terminal
Remove the old thermostat base
Check the new thermostat compatibility
Mount the new thermostat base on the wall
Connect each wire to the matching terminal
Attach the thermostat display or faceplate
Restore power at the breaker
Follow the thermostat setup instructions
Test heating and cooling functions
Secure the thermostat if needed