Before uninstalling you should stop all running services, otherwise there might be problems with existing pid-files on Linux and Mac the next time you install it. You can have a look on how to do so here.
To uninstall appserver.io on Linux, you can rely on your package management system. On Windows, you can use the normal uninstall process provided by the operating system.
Under Mac OS X, you can simply delete the
/opt/appserver folder that contains all installed files.