Turn the power off to the furnace at the furnace service switch.

Take off cover of thermostat and take a photo of current functioning thermostat wires and connections.

As a best practice, label or tape wires of current set-up. Some thermostats come with labeling stickers in the box.

If current thermostat has a common wire and wiring is compatible with new thermostat (see manufacturer's instructions), continue with the following steps.

If a common-maker or add-a-wire is needed, follow manufacturer's instructions to add a common wire.

Begin by carefully removing the screws from the old base and pulling it away from the wall. 

If the base has been painted over, use a utility knife to score around its edges first. This prevents the paint from tearing or peeling off the wall. 

To install the new base or baseplate, first position it against the wall and use a pencil to mark the locations for the screw holes. Be sure the base is level before marking.

If a screw hole does not align with a wall stud, you must install an appropriate drywall anchor. Once the anchors are in place, fasten the new base or baseplate to the wall with screws, ensuring it remains level.

To wire the new thermostat, follow the manufacturer's instructions. Refer to the picture you took in Step #2 and verify that the wiring on the new control board is configured in a similar manner. 

Ensure the wires are not over-stripped. Many thermostats include a strip-depth guide to help with this. Over-stripping can lead to a short circuit, which may cause the system to malfunction or blow the 3-amp fuse on the furnace control board.

Connect the Wires.  For Screw Lug Connections: Hand-tighten the screws snugly to secure the wires. For Press-in Connections: Ensure the wires are fully seated into the connector. The factory wire stripping length guide is particularly useful here.

Once all connections are secure, gently push any excess wire slack back into the wall and then install the new thermostat onto its base.

Once everything is connected and thermostat is covered, turn the power back on at the furnace service switch.

Follow steps on thermostat for set up.

Run the thermostat in all settings applicable to the HVAC system. CAUTION: Do not turn the AC on if the outdoor temperature is colder than 60°. Possible system damage could occur without knowing the current state of the charge.

Using a schedule template, create a schedule with client with recommended set-points.

This is also a good opportunity to talk to the client about the importance of changing their furnace filter and setting up a reminder on the thermostat if it has that ability. Be sure to set the reminder at intervals that are appropriate for the type of filter they have.

Educate client how to set schedule and change settings by programming the thermostat to a basic schedule.

Have client change temperature set-point with thermostat and phone app, adjust schedules, and set up WIFI (if applicable).