With the access cover removed, you'll see the fuel tank sending unit right there on top. It will have a wiring harness plugged into the top (this tells your gas gauge how much fuel is in the tank).
Unplug the wiring harness and move it safely to the side. If your fuel tank sending unit is screwed or bolted in place, remove the screws or bolts.
Some sending units are a "twist-lock" type. They work like the old twist-lock gas caps. You'll see a few notches along the outer ring of the sending unit. Place the tip of a sturdy flat head screwdriver in the notch and gently tap it counter-clockwise. The sending unit will rotate until it's loose. (the picture above shows the fuel tank out of the car to illustrate the fuel tank sending unit's location).
Now you can remove the fuel tank sending unit in one piece. Attached to it is a long rod with a float at the end, so you might have to try a couple of different angles to get it out.
As usual, installation is the reverse of removal. Don't forget to plug the new sender in or it won't send you anything! If your fuel filter is in the tank at this location, be sure to replace it to. If not, follow these instructions.