From what I understand the temp is factory set at 140° (typical). However, there are aftermarket kits you can get depending on the model you have.
Sample adjustable controller.
Replacement Thermostat for Suburban SW-Series Water Heaters, Gas Control
or use a mixing valve.
0215473 - Watts 0215473 - 1/2" L70A-T Lo-Temp Threaded Tempering Valve (100°-130°) on the outlet of the water heater. Pretty easy to hook up, it just mixes hot and cold water to the adjusted temp. Extends the hot water supply and gives a more even temp output.
I'm sure others will chime in that are more knowledgeable.