I have the same unit, I believe if you look on the right side of the TV, it should have a black strap that you pull towards the right, (straight out) and the lock will release. then pull the Tv down. If the strap gets stuck behind the TV it will be hard to get out, so I mounted a bracket on the wood frame that holds the strap up and keeps it from falling behind the TV
We have the same unit , and yes the above post is correct...ours didnt have the strap installed when we bought it , but we did see the metal ring that the strap is/was supposed to be and it wasnt easy to pull that lock mech out...our solution was to get a skinny arm in there "the wife" with a pair of plyers and pull straight out with assistance from me lifting up on the tv itself to take the weight of the lock.
From there I lightly lubed the lock and spring and it pulls out very easy now...very hard first time around.