Adjusting hot water heater temperature settings is something you can do for both gas and electric water heaters. The critical question is, 'How Wise Is It?', the factory settings are at a safe level.
Hot Water Can Be Dangerous
So how dangerous is hot water? At 160 degrees water can cause a second or third degree burn in a half of a second. Do you have children, elderly, infirm or handicapped individuals in your home? Caution needs to be exercised.
Most water heaters are set at the factory for 120 degree hot water. You jump from a half of a second to over five minutes before a serious burn occurs. Is forty degrees that big of a deal?
Need More Hot Water?
You may be thinking that raising the temperature is and easy way to get more hot water. In theory it is, but there are consequences. Have you made sure that your hot water heater is working properly? See the article Gas Hot Water Heater Troubleshooting for tips on what to do if you don't have enough hot water.
It is also possible that you are asking more of your water heater than is reasonable. See 'Gas Water Heater Tank Size' for information on the proper sizing of a hot water tank. Don't blame your gas water heater thermostat if you tank is too small.
Actually changing the setting is simple. You will find a dial on the front of your gas valve. Turn it toward 'Hotter' or the higher temperature to increase the temperature. Check you owner's manual for the recommended setting. It is most likely 120 degrees. There is usually a mark on the dial for the suggested setting. The danger factor goes up exponentially for each ten degree increase.
WARNING!! Hot Water Can Cause Severe Burns! Be Careful! 120 Degrees is the Suggested Setting!!! WARNING!!!