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 its terminal
Disconnect the wires
Remove the old thermostat base
Check the wall for damage or holes
Mount the new thermostat base
Pull the wires through the opening
Connect each wire to the matching terminal
Attach the new thermostat display or cover
Restore power at the breaker
Set up the thermostat according to the manufacturer’s instructions
Test heating and cooling functions
Secure any loose wires and close the wall opening if needed