As we have already heard about the public release dates of Apple's new Operating System, iOS 7. Also along with it, the company has announced a Gold Master (GM) version of the iOperatingSystem 7 to the developers.
The Gold Master version of the Operating System will be the one close to the final version, which is to be out for the public on September 18th. As this update is not available over-the-air, you'll need a pre-registered developers account in Apple, where you'll be able to download the iOS 7 GM firmware directly from the Member Center website using your Apple ID. Then continue the same steps you've followed to install the iOS 7 Beta versions, using iTunes.