You should begin by taking a look at the brand of your locks. Probabilities are that the locks are from different companies. If the locks are from different manufacturers you should buy a re-key kit for each brand. The cool thing is that the kits are easily available in the local stores. The kits cost between $8 and $10 and they come with two keys and tools that will assist you to re-key six door locks. Locksmith Staten Island is skilled to rekey a door lock efficiently.
Once you have the kit you should unlock the door and remove the door knob. This calls for you to put in the wire tool into the knob hole and depress the knob clip. You should then pull the knob off the door. When the knob is out of the lock you should push the lock cylinder out of the knob. You must then remove the retainer ring from the cylinder using a retainer ring tool that comes in the re-keying kit.