Open up your rotary phone. On the inside you will notice the few basic parts; the rotary dial, the ringer, two jacks, the hook switch and the basic circuitry which is usually encased in a metal junction-box-like thing.
There will be four wires running from the rotary dialer to this junction-box-like thing. The wires should be held in place by little more than tightened screws. Loosen the screws and disconnect the wires.
After that, disconnect the rotary dialer from the phone itself.