The most comprehensive method of ensuring security it involves removing the existing lock from the door including the handle if it s a handle lock combo and then installing.
How to replace door lock.
Use a phillips head screwdriver to unfasten the two or three screws located on the inside knob plate.
You may also need to use a wire tool or a paper clip.
Remove the screws from the old lock on the inside of the door.
Remove the two screws from the latch plate on the edge of the door and remove the latch from the opening.
Insert the pins and reassemble the lock dump out the old pins insert the new key and use tweezers or small needle nose pliers to match the new colored pins to the color code on the special instruction sheet.
Begin by removing the screws from the door knob on the interior side of your door.
Once the new pins are in reverse the steps to reassemble the lock.