When users have installed your application once (through the Android Market, or using an internal company channel), the application automatically receives the updates you publish from the website. Here is how to use this system:
Publish an update
Two kind of updates are available:
The test update.
The public update.
The test update is obtained when you click on Save in the screen designer. In this case, only the applications that have been signed with a test signature will receive the update. Use this feature when you are working on your application, in order to easily check the result on device, but when you do not want to send the changes to all of your users.
The public update is obtained clicking on Save (public). In this case, every application user will receive the update. Use this feature when you really want to send a new content to everyone that has your application installed on a device.
On the phones, updates are checked in background when the application starts. If an update is available, the following screen is displayed, prompting user if he/she wants to get this update.
The update is then received, and when it's done, the application restarts automatically, displaying the new content.
Size of updates
Update size depends on their content, of course. Depending on pictures size, the update will change. Screen configuration (everything except pictures) is really small (10-20 Kb).
Besides this, the update system is based on the last change date of your files. This means that only the modified or missing files are downloaded, saving bandwidth.