I don't know about Content Barrier specifically, as I've never used it, but applications like that typically come with an uninstaller. Now is the time to use it, if you no longer need it.
If you can't find the uninstaller, there are several tools available to remove unwanted Mac OS X applications. You can also do it the manual way - find all files related to the app, delete them, and move on.
Most well-behaved Mac OS X apps store stuff specific to you that they need in the Library folder inside your user folder, and global stuff inside the Library folder at the root of the drive. Those are the places to look.