How do you change a lock for another key?

I have a truck lock for my Demon and I have a key that it will not work. Has anyone here been able to change the lock to fit the key that I have.

Thanks in advance...................Ted
As mentioned, easy to do or have done. I do that sort of work myself, but, sometimes it's cheaper to just get a new set if you have to travel very far, or, mail the lock off somewhere. If you have no luck locally and really want to keep the factory lock, PM me for details and price.