How do I take off this metal piece

[Boombaye]

So i found this lock at the store and bought it. After taking a better look at it i cant seem to take off this metal piece.

Can anyone help me?
Sorry about pic quality, im getting a real camera for xmas.

Thanks,

Boombaye

[MacGyver101]

There's a round C-shaped circlip at the back of the lock. If you carefully pry it open a bit (i.e., make the "C" wider") you should be able to slip the tailpiece off.

Don't remove the circlip entirely, or the plug could fall right out of the lock body when you open it.