First, remove the cover by unscrewing the screws and set them aside.

The Over Temperature Sensor is located in the center of the assembly, behind the microswitch, held on by 2 screws.

Unscrew the 2 screws holding the sensor on and set those screws aside in a safe place.

Replace the old sensor with the new sensor, metal side down on the plate.

Using the 2 screws you set aside, screw the sensor in place.

Put the cover of the water heater back on using a screwdriver and the 4 screws you set aside earlier.