Before overloading your head with all the configuration stuff - let us describe to you the update workflow of the plugin. In general, without any technical details.

1. User opens your application.
2. Plugin get's initialized and it launches update loader in the background thread.
3. Update loader takes config-file from the config.xml and loads JSON from the specified url. Then it compares release version of the loaded config to the currently installed one. If they are different - we go to the next step.
4. Update loader uses content_url from the application config to load manifest file. He uses it to find out, what has changed since the last release.
5. Update loader downloads all updated/new files from the content_url.
6. If everything went well - it sends notification, that update is ready for installation.
7. Update installed, and user is redirected to the index page of your application.

And that's it. Of course, there is a little more in it, but you get the general idea on how it works.