This is actually a lot easier than re-pinning a lock without a key, it also helps that I had a new Kwikset locking door knob laying around. Not to mention, it also talks about how to go about re-pinning a different style doorknob. If you have the other style doorknob, it should be pretty easy to figure it out after reading this.
After doing this a few times, this shouldn't take more than 5 minutes to finish, but, again, it helps to have detailed instructions.
Things you'll need:
Kwikset Re-Pinning Kit
Doorknob with lock.
Step 1: Removing the Tumbler
With the part that you would put the key in, there should be a little tab behind the handle, as shown in Pic 3.
Insert the original key into the lock and turn it around a bit (Pic 4), then take the thin end of the removal tool and push the tab in. It's a little difficult to take a picture and do this, but you'll need both hands. As you press in with the tool, eventually you'll find a catch with the key, usually in a line from about 10 to 4 o'clock. if 12 to 6 o'clock is the starting point. (Pics 5 and 6).
Then, pull the handle portion off, invert it and the tumbler should fall out (if you've taken out the key). Everything should look about as it does in Pic 8.