To adjust the water temperature on the Rheem XE50M09EL55U1 Performance Plus 50 Gal. Electric Water Heater, follow these steps: Locate the thermostat: The thermostat is usually found on the side of the water heater. Turn off the power: For safety, turn off the power to the water heater at the circuit breaker. Remove the access panel: Use a screwdriver to remove the access panel covering the thermostat. Adjust the temperature: Use a flathead screwdriver to turn the temperature adjustment dial. The factory setting is typically 120°F (49°C). Turn the dial to increase or decrease the temperature as desired. Replace the access panel: Once you've set the desired temperature, replace the access panel and secure it with screws. Turn the power back on: Restore power to the water heater at the circuit breaker.