Kim, if they're glued it will be a tougher job, but not impossible.
Several methods which will help are:
Removing all drawers and cutting glue with utility knife or reciprocal saw from inside the cabinets, while working the top with a prybar.
Particularly if the top is site built, not postform, you can cut open the top with a skilsaw set to the countertop depth, and work the remains loose in a similar fashion to above. Cutting the old top into sections will be a great help if you find a thorough glue job was done.