Place a rubber mat on the ground beneath the home's breaker box. Stand on the mat, and open the breaker box's front cover. Turn off the box's main circuit breaker, as well as all individual circuit breakers. Loosen and remove the screws holding the box's inner cover in place, and remove the inner cover, using a screwdriver. Note that the terminal connections are now accessible. As an added safety precaution, do not touch any terminal connections in the breaker box by hand, especially the main power cables running into the box, and the lugs they connect to -- though the terminal connections on the individual circuit breakers will be dead, the bare power cable ends on the main power cables and lugs they attach to will still be live, and the power to them cannot be switched off.
Look for the circuit breaker that will be replaced. Loosen its terminal screw labeled "line power," and pull out the black or red wire. Loosen its terminal screw labeled "load neutral" and pull out the white wire. Follow the breaker's coiled wire to the neutral bar, loosen the terminal screw and pull out the wire. Push the edge of the circuit breaker towards the edge of the box to disengage it from the bus bar underneath the breaker. Pull out the breaker and discard it.
Switch the new breaker to its "off" position. Slide the breaker into the slot vacated by the old breaker, pushing it forwards to snap it into position against the breaker bar. Attach the black/red wire to its terminal screw labeled "line power," attach the white wire to the its terminal screw labeled "load neutral," and attach the end of the breaker's coiled wire to the spare terminal on the neutral bar. Tighten all terminal screws to their wires.
Reposition the breaker box's inner cover, tightening its screws in place with the screwdriver. Turn on the main breaker, and all individual circuit breakers. Close the box's front cover.