If you have removed the caliper, or at least moved it out of the way, it should just pull off. If not, look for a hole where you can insert a bolt to tighten down and that will then push the rotor off.
Alternatively, use a mallet to gently rap on each side to loosen it from a possibly rusted hub area.
Alternatively, use a mallet to gently rap on each side to loosen it from a possibly rusted hub area.