This is very difficult to do without damaging the shoe. Is it possible to send them back for replacements? That's far safer.
However, if they are out of guarantee or this is not possible, here's how I would proceed. Take a thin cold chisel and insert it into the gap between the heel and the shoe. You may need to insert a thin screw driver to start it off. Now gently knock the chisel through the fixings with a claw or club hammer. Peel off the liner to expose the fixing heads. You may be able to cut or pull some heads with a pair of end cutting pliers.
The object is to cut the fixings without damaging the top of the sole. This may be reinforced with a metal plate and the shank fixing usually has a rivet. But, while cutting the fixings, it is still very easy to damage or tear the paperboard sole. Don't be tempted to pull the heads through. That may tear the board. try to cut everything with a sharp chisel, end-cutting pliers or a hacksaw blade.
http://www.edirectory.co.uk/pf/image...ages/19490.jpg http://www.7volts.com/tool1.jpg
Only use top quality tools!
You'll probably find that the board will be damaged but, if necessary this can be reinforced with a thin piece of tin plate cut to shape and drilled to take the new fixings. The other point of damage may be on the heel where the chisel first went in. This can be repaired by filling and painting/covering.
The existing fixings will either be nails, metal plate with tangs or screws. If you find screws, of course unscrew them from inside. You wont be able to reuse the nails etc. The new fixings I would use are 6 Tek screws or chipboard screws fixed in drilled pilot holes. The plastic of the heel is very hard and although these screws can cut their own thread, they wont be able to deform the plastic to make rooom for their shank, hence the need for pilot holes.