Turn off the main breaker supplying electricity to the service panel. The main breaker is at the top of the panel.
Remove the cover from the service panel to expose the circuit breakers and the electrical wiring.
Confirm the disconnection of electricity using a two prong electrical tester. Touch one prong from the tester to a screw on the back of any breaker holding a red or black wire and touch the other prong to the metal service panel box. The tester should not light up or register any wattage. Do not test using the dryer circuit breaker because this breaker needs replacing and may not register correctly.
Loosen the two set screws holding the black and red wires in the breaker. Pull the black and red wires from beneath the screws. Grab the breaker and pull it from the service panel.
Install the replacement 30-amp double pole breaker into the service panel. Slip the back lip of the breaker under the slot that holds all breakers in place. Push the front of the circuit breaker over the bus bar at the center of the panel.
Slip the black wire and the red wire under the two set screws at the back of the breaker. Tighten both set screws, holding the wires firmly in the breaker. Replace the service panel cover and turn the main breaker to the "on" position.