I need to replace toilet flange it is cast iron it is hooked to 4 inch cast iron pipe how do I remove pipe from elbow

Show us a picture.

With a small drill bit, drill a series of holes in the led around the joint until you have removed enough of the led to grasp the remaining led with needle nose pliers and pull it out.

Why do you need to remove the flange? If one side's broke they make a repair part (see image) for a easy fix. But if you have to remove it follow Harolds advice and get back to us. Good luck, Tom