The autoupdate can be done from your application, or using an application launcher.
Since it's an online auto updater you will need a set of server that your system can contact to retrieve the update information (one server is just completely too dangerous).
The information can be a simple xml file (don't forget that once your device is in the wild, you can't change the xml format).
Then you will have to download the new files/archive and overwrite your system with it. Depending on your software you will have to restart your system and/or application.