Ok, facing the unit there should be a small square plate. Normally blue. take this off with the two screws that hold it on. You may want to kill the power to it first.
When you get the cover off pull the insulation back some to expose the thermostat. With a flat head screw driver turn the head screw in the center to wards the higher degree temp you need. Normally about 140 is high enough. There will be temp numbers to guide you. Put the plate back on and your ready to go.
If you have any problems just ask for me. But this will do it and save you a plumbers bill.
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