How should I remove a raised concrete pad on my basement floor?
If it was poured onto an already existing slab, I would try separating it from the slab first to see if it can be broken away and leave the floor intact.  Note:  The pad should weigh about 815 pounds (370 kg) so light duty efforts are inappropriate.

Obtain two heavy steel digging bars like this along with some scrap 2x4s or similar.  With heavy gloves on, try to wedge the pointy end into the joint between the pad and floor by holding it mostly horizontal, but still a down angle of 30&deg; so the point is against the floor and firmly swing it into position.  Or use a hammer and cold chisel to chip out a notch right next to the floor so the flat end of the digging bar can get a grip underneath the pad.

If you can establish a catching point, place a 2x4 3&ndash;4 inches away from the edge and use it as a fulcrum to lift the pad.  Recall leverage basics:  If you push down on the far end of the bar with 100 pounds force and the fulcrum is one-tenth the distance from the other end, that is a 10:1 force gain, so you will be applying 1000 pounds of lift.  If you can get it off the floor, insert the other bar with another (or a shared) fulcrum to raise it 1.5 inches off the floor.  Slide in a 2x4 to support it at the lifted edge (this probably requires one or two helpers) and withdraw the bars.

Once the pad is mechanically separated, have some Wheaties and then swing a heavy sledge hammer (15+ pounds) approximately one-third the distance away from the supported edge.  It is easiest to crack the pad by starting close to the edge.  Don't be discouraged if you don't see any cracks even after a dozen husky whacks&mdash;especially with six inches.  Each impact is being absorbed and is weakening the pad.  However, while it is intact, it is strongest.  Persist and it will soften, crumble, and eventually break.  After the first crack, it will become much  easier to break up.

Break it into convenient-to-carry pieces and dispose.  Clean up underneath.  Probably the floor will be in good condition if the pad was added much later than the floor.  Otherwise, you might have to sand down bits that stick and smooth the floor.