One source would be the Mfgr/Owner's Guide. If you don't have one, I'm sure one can be had by contacting the mfgr. I'm sure there's info on this right on the heater's label.
Other than that, all I could find was the following: Drain hot water heater; remove sediment from bottom of tank; clean and adjust burner surfaces. (If you know what you're doing, then you're on your way!)