Turn off power to the HVAC system at the breaker and thermostat
Remove the thermostat cover
Take a photo of the existing wiring
Label each wire by terminal
Loosen the terminal screws and disconnect the wires
Remove the old thermostat base from the wall
Check the wall for damage or old anchors
Install the new thermostat base level on the wall
Reconnect the wires to the matching terminals
Tighten the terminal screws
Attach the thermostat display or cover
Restore power to the HVAC system
Set the thermostat to the correct system type and settings
Test heating, cooling, and fan operation
Secure the thermostat and patch any wall holes if needed