If the key way looks similar to this....
Then I can help you, firstly open the padlock up and then where the shackle pops out look down the hole and you will see a screw, undo that and the cylinder falls out, after that you need to re-pin the lock, I made a video a while back showing you how to do that...you can dowload it here...
http://www.arach.net.au/~cw.chookysworld.com/Re-Pin.rar
Hope it help you, keep us informed....
If its not like that padlock, there is a way you can drill out some retaining pins and you can remove the plugh, or you can re-pin it while its still in the lock, but I have never dont that before, all I know is that you needa 3.2mm drill bit and some 3.2 mm thick brass rod, to fill the gaps after youve drilled them.