How hard it is depends on the install. Now I have an atwood
The element is on what I call the "Back side" (where the pipes connect) just above the relay under some insulation. You Drain the tank, unhook the wires, unscrew it Take it to LOWES or not.
You have two options 1400 or 1500 watt 120 volt or I choose a 1500 at 240 volt (375 watts at 120) and screw it back in Hook up the wires. tape the insulation back in place done.
Why the 375 watt.... Well I went a long time before I tripped a 30 amp breaker. A few sites I still trip 30 amp breakers but they are few and far where as they used to be frequent. 375 is close to what the HOtt Rod runs (400) and your fridge (350) in case you wonder. Takes a bit longer to het 'er up but if I'm in a hurry there is always PROPANE. the stuff that keeps you warm.