Interior door locks are a bit different than your entry door key locks. The outside door knob has a small hole and the inside handle usually has a thumb knob that you turn to lock the door. Instead of a lock cylinder, the inside door knob has a flat metal or square tab that will fit into the latch assembly inside the door. After removing the old lock, you can install a new door lock in 30 minutes. Interior door locks are available at home improvement centres.
Set the new door lock latch assembly into the edge of the door and test the fit of the latch plate. The latch plate should fit flush to the edge of the door. If the plate does not fit flush, trace the outside of the plate onto the door edge with a pencil and pull the latch assembly out of the door.
Mortise the area within the trace area with a wood chisel and hammer. Remove the wood within the trace area and as deep as the thickness of the latch plate. Insert the latch assembly into the door edge and seat the latch plate flush to the door. Secure the latch plate with wood screws and a Phillips-head screwdriver.
Position the strike plate over the existing hole on the door frame jamb. The strike plate hole should fit around the existing hole in the wood and the strike plate face should be flush with the jamb. If necessary, mortise the area for the strike plate as you would for the latch plate. Secure the strike plate to the door frame jamb with wood screws.
Set the outside door handle into the door from the outside. The sleeves of the handle should fit into the two round holes on the door latch and some also have a sqaure peg that will fit in the centre of the latch assembly.
Slide the inside door handle assembly into the door from the inside. Secure the handles together with the two long screws. There are two long screw that are threaded all the way that come with your kit. The screws insert through the two holes on the inside knob faceplate and into the sleeves of the outer handle. Tighten the screws with a flathead screwdriver.