2000 Chevy Silverado

Disconnect the battery.
Unhook the electrical connector(s) to the fuel pump. (You may have one connector or two depending on the code on top of the sending unit).
Use a wire brush or stiff bristle brush to remove all the dirt and debris on top of your tank/sending unit.
Disconnect all fuel lines (put rag under lines, there will be some fuel leakage.)
Take a hammer and a blunt chisel and rotate the locking ring counter clock-wise (careful not to cause any sparks).
Once the ring is off (can be arduous) ensure you brush/blow away any rust or debris from the retaining ring.
Lift the pump/sending unit out of the tank.
You can re-use the retaining ring if it is not too corroded or damaged from removal, otherwise purchase a new one (does not come with new sending unit).
Installation is reverse of removal.