Note:If you’re downloading the firmware files using Safari then ensure that auto unzip feature is disable or use Chrome or Firefox.
Connect the devices running iOS 7 beta version for your computer.
Launch iTunes and select the iOS device from the upper right corner, to the left of the button on the iTunes Store.
Hold the Alt/Option key (Shift key in Windows) on the keyboard and click the Restore button, iPhone/iPod touch in iTunes. Note: If you did Find My iPhone is enabled then it will prompt you to turn it off before you restore your iPhone (it is one of the features of iOS 7).
still pretty tight.
Select the ipsw file you downloaded earlier.
iTunes will announce that it will erase and restore your iOS device on iOS 6. xx and will check the restore with Apple.
iTunes will now restore your iOS device on iOS 6. xx
After the restoration, the iOS device will restart. Then you will see the “slide to set up”. Follow the steps in the Setup Assistant iOS.
Then you can restore your device from a backup if needed.