Turn off power to the water heater at the circuit breaker
Remove the access panel covering the thermostat
Remove the insulation and plastic safety cover
Locate the temperature adjustment dial on the thermostat
Use a flathead screwdriver to turn the dial to the desired setting
Set both upper and lower thermostats to the same temperature if there are two
Replace the plastic safety cover and insulation
Reinstall the access panel
Turn the power back on at the circuit breaker
Wait several hours for the water to heat
Test the water temperature at a faucet
Adjust again if needed
Keep the temperature at or below 120°F for safety