Unlock the door for which you want to change the lock mechanism. Put the key in the lock hole and turn it anti clock wise to open. If key is struck or the lock does not budge, enter the car through another door and open it manually from inside. Lower the window of the door if the electric motor is working or do it manually by the handle. After lowering the window, take off the handle from the door.
Depending on the make and model of your vehicle, there will be different number of screws on your car door. Consult your car’s owner manual to find their number and position. Remove the leather covering on top of the door to expose them and use a screw driver to open the inner panel of the door. Then remove the underneath screws from the door tray and armrest area. After that remove the wooden panel from the door such that the other side of the door becomes visible.
Take off the bracket covering the door lock cylinder with the help of small size tweezers or needles. There may be pocket size screws holding the bracket in its place as well depending on your car. For that you will have to use pencil straight screw drivers to open the bracket.
Underneath the bracket there will be 2 or 3 screws which hold the door lock mechanism in its place. Take out the lock and clean the inside of the door with an air blower. Use a cloth to remove grease or any other lubricant from the door chamber.
Assemble the new door lock mechanism and put it in its stipulated place and affix it with the same set of screws. Follow the steps in reverse order to pack up your door again.