Lift the trim plates carefully, and remove all visible trim screws with a Philips screwdriver. Remove the edge plate screws and trim cover. Remove the strike plate screws and plate if you are replacing the trim.
Remove the edge plate mounting screws with a Philips screwdriver. Pull the door trim and knobs or levers from the door panels. Remove all visible lock case mounting screws from the door edge and panels.
Pull the lock case from the door edge. Measure the lock case, trim pieces and all lock holes in the door for replacement parts. Take the case to a professional locksmith if you cannot find a suitable replacement at your local home improvement store.
Slide the new lock case into the door edge. Install all mounting screws in the door edge and panels with a Philips screwdriver.
Insert the knob or lever into the exterior door panel, and secure it with mounting screws and a Philips screwdriver. Install the interior knob or lever, and secure it with mounting screws. Install the edge plate and screws.
Replace or slide the lock trim over the knob assembly, and then secure it with trim screws.
Reinstall the strike plate and screws.