Now you can test it and put it back together. If you can't seem to get the key to turn, move the pins back to their original places except the the con...
Have you ever given someone a key to something but then later on decided it wasn't such a good idea and you fear that they have copied it, I recently had that problem. There are plenty of lock smiths that will re-key a lock for a fee or you could go out and buy a new door knob. I was running low on cash and decided to take the knob apart and see if there was a way to change the pins (and my key) in a way that the original key wouldn't work. This is my first instructable and is based on what I did. But first, I am NOT responsible for any damage you do to your door knob.
Step 1: Remove the knob
My door knob has a small hole between the part that rotates and the part that attaches to the door (refer to picture). All door knobs can be taken apart, yours will probably be different than the picture. When the door knob is turned the correct way there is a button that can be pushed to release the knob. Remove the knob but remember how it came off.