rear wheels

Are you saying the brakes are locked? Do you have rear drum brakes? Have you removed the rear tire? With drum brakes, on the back side if backing plate there is usually a slot where you can use tool to release the tension on the drum brakes, so you can remove brake drum. You need to safely raise and support the vehicle. It's ok to use jack to raise the vehicle, but use proper jack stands to support the vehicle when you work on it. Safety is your responsibility. The vehicle needs to be on level pavement to use jack and jack stands. It's never totally safe working under a vehicle.