Pull the square outward from the back of the lock, jiggle the key and the key comes out as does the latch and latch.
To reassenble, push the latch in until it clicks, look into the lock cavity and push the latch just enough to see the indention in it, push the cylinder in (with the key in it) and the peg on the back of the cylinder lined up with the indention on the latch, turn the key and it will click into place.
Believe it or not, this is the second time today I have told someone how this is done.
Good luck!