on most tv wall/ceiling mount brackets, there will be a single screw located where you can access it (usually one side or the other, rarely on the top or bottom) so it can be removed and replaced as needed.... once the locking screw is removed, the tv should lift up and come free of the mount bracket... make sure you disconnect the cables before lifting the tv off the bracket so you arent trying to balance the tv in your arms while trying to disconnect them.
depending on the model, some mount brackets have a lock to keep the arm from swinging when you dont want it to....