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 letter
Remove the thermostat base from the wall
Check compatibility with the new thermostat
Attach the new thermostat base to the wall
Connect each wire to the matching terminal
Mount the thermostat display or faceplate
Install batteries if required
Restore power to the HVAC system
Follow the thermostat setup instructions
Test heating, cooling, and fan functions
Secure the cover and clean up the area