If you mean the steel wheels are stuck to the front rotor/hubs and/or the rear drums give them a good soaking with your favorite rust bust stuff or ATF and allow a day or two for it to soak in. Then with the car jacked up (with jack stands supporting the car under the jacking points) loosen the lug nuts so there's a gap between them and the wheels (you don't want the wheel to come flying off). You'll need a hefty hammer to smack from behind. If you smack the tires you'll need a heavy sledge hammer to effect some real force. A block of 2x4 will protect the wheel rim edges where the force will be most effective.
If you mean the wheels will not spin due to the brakes being locked up you may need to drive a wedge (screwdriver) between the pads and the rotors to force the pads/pistons back. The rears may be more of a challenge if you had applied the handbrake and that's now seized.
Be sure to keep a few cold ones handy as reward for your hard work. -- Dave