As an ex Water Supply fitter I would advise you check the Anode annually. Water quality fluctuates over time due to changes in the chemicals in it, a bit too much Chlorine or a change of source for instance and the Anode takes a knock. If is down to 10/15%, change it. They are not expensive when compared to a new tank and can more than double the life of your Water Heater. At the risk of upsetting some in the trade
. you don't need a plumber, unscrewing an Anode and replacing it (with a new sealing washer) is not rocket science. Like the man said, turn off the water, turn off the power, drop the pressure, and unscrew. Forgot to add, while you are at it, pull the lever on the pressure release valve before you turn the water off and give it a quick squirt to clean it out, if it won't close properly and drips. Have it changed.