Typically, getting an iOS device to update is as easy as plugging it into your computer and hitting the Update button in iTunes—or even easier if you have an iOS 5 device, as you can handle the update directly from the Settings app.
But what if you need to downgrade your OS, or install an Update image that iTunes can’t retrieve from the server—such as the just released iOS 6 beta? Doing so is easy.
Simply connect your device to your PC or Mac, make sure you have the latest version of iTunes installed and the necessary update image downloaded, click on your device in the iTunes sidebar, and when the main tab appears, hold the option (on Mac) or shift (on Windows) key in and hit the Update or Restore button, then choose the location of the update image.
