The sending unit is held in place with a lock ring around it's perimeter. It has to be driven counter clockwise by hitting the edge that sticks up with a punch. A brass punch will not cause sparks that could lead to an explosion. Not likely, but could happen.
I'm not condoning it, but I've seen them driven off using a large flat blade screwdriver and a hammer.
If you have a four point lift, the rear end WILL hang down, allowing easy access to the tank and sending unit. Much easier than laying on a hard concrete floor!