I know the top has to come off but i have tried to remove it and there is still something holding it down.

You have two options. They just set into the cut out but have to be caulked in place to prevent leaks, and cleaning liquid from getting between the server and counter. To remove ussually requires a thin blade be run around the unit edge to break the silicone. But you can also just remove the two nuts on the studs that mount the heater and…