How to restore or update your iPod/iPhone/iPad:
After downloading the desired firmware below, you can shift-click (PC) or option-click (Mac) the Restore or Update buttons in iTunes. A file dialog will open and let you choose the downloaded ipsw-file.
Note: Your browser may change the ipsw-file into a zip-file. In that case, just rename it to end in .ipsw and iTunes will accept it.
If you don't know what device or specific device generation you got,
click here.
By clicking Download, you will be redirected to
an Apple Inc. server. The list of available firmwares is
automatically updated and always the most recent version.
Find