How do I install the Honeywell RTH5160 thermostat?

Start by turning off power at the breaker box and documenting your old thermostat's wiring with photos and labels. Remove the old thermostat's faceplate, then disconnect the wires using a screwdriver. Insert the wires through the UWP mounting system, set the R-switch position based on your wiring (up for 1 R-wire, down for 2 R-wires), and connect all wires to their matching terminals. Install two AA alkaline batteries, attach the thermostat to the UWP, and turn power back on.