What brand of heater do you have - Atwood, Suburban or perhaps an American? And what model?
Most Atwoods have separate thermostats for LP and electric operation. The t-stats are mostly fixed temperature units but Atwood offers a couple different part numbers with different temp ranges. They also have one that is adjustable. If you have an Atwood, get the model number and check with a dealer or parts supply warehouse for t-stats that will fit your model. The LP mode t-stat is pretty easy to change but the electric t-stat may not be readily accessible (its on the back side of the tank). A few Atwood LP only models have an external, adjustable t-stat right from the factory, but you would probably have noticed that since it's right by the pilot controls.