1. Download the iOS 7 official release. ipsw. from your developer account as shown in left panel .People who are not developers they need to get copies of ios7 official release by any other sources.
3. Take a complete backup of device.
4. In iTunes click on the iPhone option in the upper right and when you see the Restore and Upgrade options you are on the right screen.(See snap on left )
5. Click check for updates holding shift key on windows or alt and option key together in case of mac.
6. Navigate to the downloaded .ipsw file and click.select it.
7. Complete the iOS 7 upgrade
8. After completion of restore you will be on official iOS7