Before you uninstall, you might want to deactivate your license first. That will free up your license to be used on another server. If you just upgrading to a new version of Otto, you can leave the license activated.
You can uninstall Otto by running the uninstaller that is in the Otto application directory.
You can then install a new version of Otto if you like right over the old Otto folder. Or you can get rid of the folder.