Do I have to get a new mount if i buy a new TV?

I want to get my 42' TV mounted to the wall this weekend but in the future I would like to get a bigger TV. When a TV is mounted is it on a hook or is it actually screwed into the wall? Like can I leave the mount up and switch out the TVs or will I need someone to come re-mount the new TV? FYI: I'm getting the articulating mount (swivels and literally pulls away from the wall) if that makes any difference at all. Thanks for answers in advance, have a great Wednesday.