How to Replace a Door Lock

Doorknobs (also called locksets) come in many styles and degrees of security.
The majority of them are fairly easy to take apart or install but if the locking mechanism is particularly complex, such as for a high security door, you'll probably want to go to a professional locksmith instead of attempting the job on your own.
The household lockset is a fairly basic piece of equipment, but it can come in many different styles. The two most common are the deadlatch and the spring latch. Locksets with spring latches are easier to install, but deadlatch sets tend to be more common because they offer more security. Here are the basics of each:
Deadlatch lockset:
Outside knob has the keyhole.
Inside knob. Faces inside and usually has the locking button.
1. Start by removing the inside knob. Normally there are two exposed screws holding the knob in place, simply remove the screws and the inside half of the lockset will pull off, the outside portion of the lockset is also free and can be removed simply be pulling it out.
If there are no visible screws, look closely at the stem which is the straight shaft just behind the knob itself, and you should see a very small button in the side of the shaft. Press this button (try a flathead screwdriver), then pull the knob toward you. It should slide off the stem.
2. Next, remove the cover by finding a small notched opening on the cover's outside edge. Slip the top of the screwdriver into this space. Angle the screwdriver's handle toward you and the cover should pop off easily.
3. Now you will see two screws that are holding the lock onto the door with a faceplate. Remove the screws, faceplate and the lock can be removed.

Assemble the lockset :
Assembly is basically the same process as the dismantling, except it's done in reverse:
1. Insert the lock into the opening from the outside, Line up the opening in the locking mechanism with the latch.
( The latch is the spring loaded piece in the edge of the door that engages with the door jamb to secure the door )
The latch's spring extensions should slip and secure easily into the opening. Test it by turning the knob.
2.Install the faceplate with the two screws
3. Slip on the cover and snap it over the bent wire latch that holds it in place.
4. Slide the knob onto the shaft, depress the little latch on the shaft so that the knob slides over it, when in place the little latch will pop up into the slot and hold the knob in place.
5.Finally, give the lockset a thorough test: try both knobs and lock and unlock the door (if it has a lock). Make sure the bolt engages the strikeplate smoothly and there you have it!