RapidMiner Studio stores plugins installed via the marketplace from within RapidMiner Studio in the .RapidMiner/managed folder in the user home directory. You can install new plugins via the marketplace inside the application or by copying the plugin into the lib/plugins folder in your RapidMiner Studio installation directory. To uninstall a plugin, go to “View” -> “Manage Extensions” and select the red 'X' to remove it.
Note that to uninstall a plugin installed from the marketplace manually, the extensions.xml inside the folder has to be updated as well by removing the
<extension> ... </extension>
element for said extension.