[LazyPup]

THE BAD NEWS IS: it is nearly impossible to remove a leaded cast iron flange without damaging it.

THE GOOD NEWS IS: you don't need to remove it.

Whenever it is necessary to raise the height of the closet flange because the flooring is built up you can get a "Build-up flange" which is a flat plate of PVC material made in the same shape as the top of a closet flange.

To install a build-up flange you begin by inserting your closet bolts into the existing cast iron flange and secure them in place with "fainstock clips". The build-up flange is then laid on top of the existing flange with the rubber gasket side down so the gasket seals between the buildup flange and the existing closet flange. You then use a wax ring and attach the toilet bowl in the normal manner and when you tighten the closet bolts it is all held together.

See attached illustration.