[billyboy]

Get a tester for ac voltage. There are several different kinds.Shut off the main breaker, the big one up at the top. Pull the face off the panel. Test the buss bar serving the one side of the breaker. Connect one leg of the tester to it and the other leg of the tester to the neutral buss which has white wires coming off of it. Should show no current. Double check in the house with several lights and or appliances etc. When your sure, take the wires off of the offending breaker and then pull it out. They have several different locking means depending on the brand of box and breaker. Replace breaker. Reattach wires to screw terminal.Depending on how much slack wire you have, you can attach wire with the breaker out or it might need to be in place if the wire(s) are too short. Put face of panel back on and turn on main power. Then turn on the new breaker. All your timers and controls for heaters and AC etc. may need resetting since the power was off.