Remove the thermostat from the back plate by pulling the thermostat straight out and off the wall.
Take out the existing batteries.
Insert the new batteries following the specified polarity markings on the thermostat.
Return the thermostat to the wall plate by pressing the thermostat body firmly into the back plate mounted to the wall.
IMPORTANT: Verify that the pins on the body are correctly aligned with the back plate. Failure to do so could cause damage to the thermostat.