As I recall, my electric water heater (80 gallons) had 2 elements, one towards the top, and one towards the bottom. Each one was held in with four bolts, and there were one or two wires on the outside. There was also a small cover over the outside of the tank, concealing the elements.
Make sure you turn off the power for the tank, at the breaker. Donít just turn down the control on the tank. Then, shut off the water to the tank and drain the tank completely.
Remove the covers. Remove the wires (note their location). Remove the bolts. Gently pry loose the element. Remove any excess seal that may be still stuck on the tank.
Now is a good time to look inside the tank and check for problems like too much sediment at the bottom, a rusting down pipe, or rust spots in the liner. You can flush out much of the sediment, and the down-pipe can also usually be replaced, but if it generally looks really bad inside, you may be better off getting whole new tank.
The big thing is how the elements get mounted. The part of the element going in the tank looks like a loop of small metal tubing. Some have double-loops, or twists, but basically the element gets mounted so the main loop is parallel with the tank. In other words, where the loop connects to the mounting flange, one part of the loop is above the other. Otherwise, constant heating and cooling of the element will cause it to flex, and fail much sooner.
Attach new seals to elements, add sealant, if required, insert elements, replace bolts, replace wires, replace cover, done.
As I also recall, the new elements came with detailed instructions, and the new elements themselves had little arrows indicating how they were to be mounted.