I have the same model on my 2005 CD25. There are 2 "thingies" on the front of the unit with wires going to them. One is pretty obviously the heating element (part #73129); the other is the "hi-limit" thermostat part (#74563). It is the thermostat that tells the heater when the water is hot enough to stop heating. If this thermostat is fine, there is no way to change the "set point" temperature -- the temperature is the temperature; but if it's bad, the heater may just keep on heating.
I replace both these parts 2 years ago. I wanted a 1000 watt element (less load on generator), and I replaced the thermostat too for good measure (the part was relatively cheap as I remember). Note you do not have to drain the tank to replace the thermostat; it does not penetrate the tank.
P.S. You might be able to buy a different but compatible thermostat with a lower set point.