The ignition lock cylinder is the device you turn the ignition key in. If you change an ignition cylinder, you will be changing the ignition key as well because every cylinder requires its own key. A replacement cylinder for a specific model, such as a Ford Focus, will include a key that will work with that cylinder. Changing an ignition cylinder on a Ford Focus is slightly easier than changing other manufacturers' models because Ford's models don't have an extra wire connecting the cylinder to the system.
Disconnect the ground cable from the battery's negative terminal. Set it aside where it can't accidentally snap back onto the terminal.
Remove the lower panel of the dashboard below the steering column by removing its screws and releasing the fastener. Disconnect the upper shroud of the steering column by releasing the clips on each side with a thin flathead screwdriver.
Detach the audio control switch from the column if one is equipped. This is a small remote control-like device sticking out of the column. Use the screwdriver to release the switch's plastic locking tang at the bottom and then unplug the electrical connector.
Release the locking lever on the steering column so the column is loose. Remove the screws for the lower shroud on the column and remove the shroud.
Insert the key into the ignition switch and turn it to the left so it is in position one--the accessory position. Depress the detent spring (inside the small hole at the top of the cylinder) with the screwdriver and remove the cylinder and key.
Place the key for the new cylinder within the cylinder. Insert the cylinder into place within the steering column, lining it up so it will be in the accessory position. Make sure the detent locks into place. Turn the key so the cylinder is in the off position and remove the key.
Replace the lower and upper shrouds to the steering column, reconnecting the audio control switch in between if needed. Put the dashboard's lower panel back in place with the fastener and replace the screws. Reconnect the ground (negative) battery cable.