Updating custom firmware in itunes
1 - Launch i Tunes (make sure i Tunes is up-to-date) 2 - Connect device to computer 3 - Select your device in the list (e.g.: Filip’s i Phone) 4 - click the “summary” tab 5 - hold the Alt key (on Mac OS X) / the Shift key (on Windows) and hit “restore” (as shown in the screenshot below) 6 - i Tunes will show a dialog allowing you to select the IPSW file you want your device restored to 7- select the IPSW firmware bundle you want to restore to and hit “choose” 8- be patient and wait for the installation process to be completed by i Tunes Here’s another important note (which Windows users should pay particular attention to; also, this is something that only applies if the user chooses to look for the desired IPSW file on the Internet). For example, Microsoft’s Internet Explorer does this, if used to download the firmware bundle. Instead of wasting time switching web browsers, just rename the file to end in “.ipsw” and i Tunes will accept it.
Softpedia does not encourage downloading i Phone / i Pod update / restoration files from the Internet. Unfortunately, the company allows customers to download the latest version of the software only, but device owners can choose to save the older IPSW files they’ve previously downloaded and use them to revert to an older version.
It is currently believed that it makes a new IMG3 container for the image, and discards the old one before flashing to the correct place in NAND/NOR.
There are some problems with the leaked versions, because they almost always aren't the latest version.
Whichever way you choose to ultimately obtain your update / restore file, the process of updating / restoring your device to it is basically the same. You don’t even need to follow a guide, or anything like that, although Apple has provided several, just in case something goes wrong.