Nokia has pushed Amber update to all of its Lumia windows phones, but AT&T, which is the touted as main Windows Phone network provider in US is still testing it. One reddit user contacted Microsoft Store’s employee and he was told that AT&T will be seeding it the GDR2, a k a Amber update in less than two weeks. He mentioned August 26 in his post.
If you cannot wait, you can download and install it now on your AT&T Lumia 920. However, we encourage to wait for another 10 days as the aforementioned unofficial way erases all data on your phone. Going the official way also would not void the warranty. via reddit