A double pole circuit breaker means that it was a 240 volt electrical circuit delivering whatever amount of amps shown on the circuit breaker handle, 20, 30 etc. The breaker must be matched to the electrical wire size. For example a 20 amp circuit breaker protects a #12 wire and a 30 amp circuit breaker protects a #10 wire. To change it to a 120 volt circuit simply take the white electrical wire that is attached to the circuit breaker and move it to the neutral bus bar leaving the black electrical wire where it is, you will see in the box where all the white wires are attached. I suggest that you replace the circuit breaker with a single pole type. Black electrical wire to circuit breaker, white wire and bare ground to the bus bars on the sides. Be sure to get the type of circuit breaker that matches your circuit breaker box, GE, Murray, Square D, etc.
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