I have a standard 37" x 22" granite top with sink on top of a typical bathroom vanity. The sink is cracked and a corner on the top is knocked off. I've found many tops with sink available that will fit perfectly, but I do not know how to get the old top off. I have of course tried to pull up but it's stuck on there so that didn't work. There are no screws or bolts holding it either. Since i want to preserve the vanity I can't just pry it off with some sort of crowbar. Anyone got good ideas in this regard or do I have to replace the vanity also?
Use a long sharp knife, like a carpet/flooring knife, to slice through the caulking or construction adhesive that was used on the top of the vanity when the sink was set onto it. Then yes, use a lifting/prying strategy that minimizes potential for damage to the cabinet. You may need to slice, lift a little, slice some more, lift a little more, slice...
After you've undone the plumbing below, I'd use quick support rods or 2x4s cut a little long to push up on the bottom of the sink and help to lift it out. While the quick rods are pushing up use a long knife and slice any silicone that is holding the sink to the counter.
If you use the quick support rod then you can just turn the rod to increase the force applied.