If plugins won’t uninstall under the plugin management tab, you can easily delete them from the plugins folder in the web file manager.
Overall it’s easier to find plugins online and upload them into AMP, as the third party service AMP uses can be a bit limited at times.
To change the server version you can just look under the instance’s “Server Settings”. If you don’t see the version you’re looking for, you can stop/start the instance to update the version manifest.