Apple released the fourth beta on 8-6-12 iOS 6, the mobile system will be available to the general public in the fall. This version is still reserved for developers and it is obtained from the settings of iPhone or iPad. Count 280 MB for an iPhone 4S, 260 MB for an iPhone 4 or the new iPad.
The Apple TV is also entitled to an update, as well as Xcode, the development tool offered by Apple which is version 4.5 DP4. This version must be retrieved from the Developer Center.
Apple's servers are a little trouble, take your troubles patiently ...
