Once you get to it you might need to order this:
https://www.amazon.com/Camco-09951-P.../dp/B00103PNTO
Mine was so tight, and so far into the access space, that I couldn't break it loose with my residential water heater element socket. The Camco socket and an extension got it easily.
Also be prepared with rags and some low cut containers that you can fit in there, even if you drain the heater there will be quite a bit of water when you remove the element. A wet-dry vac helps too, put a length of tubing on the vac and you will suck a lot of calcified junk out of the bottom of the tank..
On my Via the water heater is directly below the furnace and access is thru the furnace cold air return louvered panel under the wardrobe. Good luck and let us know how it turns out!