If the keel
is cast iron it would have been drilled and tapped to receive the keel studs. You may be able to double nut the stud and back it out of the keel. Use penetrating oil
on the studs and let it soak in for a few days. Back out the studs one by one. They should be 6 to 8 inches long. If the exposed end of the stud is rusted it may snap off. That will be a problem because you will then need to drill out the stud, as has been said. Good luck and may the force (torq) be with you.