The knob lock usually comes apart pretty easily. The knob where the key hole is, you should be able to spot a little hole somewhere on the side towards the "neck" (that's what I call it cos I forget the proper term) of the knob.
Once you turn the knob in the right direction (left or right depending on the lock) and hold it in that turned position, you can insert a wire tool into that hole to depress a retaining pin like in this picture,
http://hostedmedia.reimanpub.com/TFH/St ... LOC_01.jpgAs you keep that retainer depressed you will need to pull on the knob and it should come off the entire assembly. Depending on the quality and age of the lock you might need to play with it a little for it to come off but that's the gist of it. Also the wire tool you'll be using to keep the retainer depressed can actually act as a retainer from the outside which could make pulling the knob off a bit more trickier, but you should be able to do it fairly easily.
The whole rekeying article is here btw if you need it,
http://www.familyhandyman.com/DIY-Proje ... ep-By-Step
