UpdateKit is a free and open source framework that allows developers to notify the users of an iOS 5.0 or more application that an update is available, and to offer them to install the update.
The version number is automatically fetched from the App Store. When an update is available and the user accepts it, the App Store application is opened on the application update page.
If you are still in beta and have not yet published your app on the AppStore, you can activate the manual mode. It allows you to set the version number and download url.
Detailed instructions on how to use the UpdateKit framework within your own iOS applications are available HERE.