There are two thermostats on your water heater. One is the normal cycling thermostat and the other is the high temperature cutoff stat.
The two stats are behind the gray cover in this photograph. If you notice there are 4 wires with red colored spade connectors right in the center of the water heater. Two of those wires connect to each of the thermostats.
The bad news is that you will have to look at the thermostat to see if it is adjustable. Most are not, but are fixed temperature thermostats. You can buy a lower temperature one or an adjustable one from your dealer to lower the temp if your OEM one is fixed temp.
The thermostats look like these
Joe & Shelly, Justin, Tyler, Alyssa | Butler PA
2008 Tiffin Allegro Bus 43QRP|Cummins 425|Honda CRV