The lock cylinder is held in place by a little spring loaded pin. It's on the inside end, towards the bottom if I remember correctly. I haven't pulled one apart for some time, so I don't remember if there is easy access to it. As a minimum, you have to remove the knob assembly to get to it. Not difficult; just remember where the wires go. (And, disconnect the battery; these wires are HOT!) Once you remove the assembly, I THINK there is a hole where you can push the pin in, and then just pull out the lock cylinder. You might have to have the key in the lock to do this.
Sorry, I know this is vague, but it's been a while and my memory isn't what it once was.