1. Delete the previously down*loaded software update file which you will find in this loca*tion depend*ing on your system:
Mac: /users//Library/iTunes/iPhone Soft*ware Updates
Windows XP: System Drive:/Doc*u*ments and Settings/Application Data/Apple Computer/iTunes/iPhone Soft*ware Updates
Windows 7: System Drive:/Users/Your Username/App Data/Apple Computer/iTunes/iPhone Software Updates
If you faced the error while upgrading your iPad or iPod, the last location path will change:
../iTunes/iPod Software Updates or ../iTunes/iPad Software Updates
2. Now, restart iTunes & begin the update again. This time iTunes will download a fresh copy of software update file.
If you’re trying to restore by using the downloaded iOS 7.0.2 IPSW file:
1. Re-download the IPSW file.
2. Now, restore to this newly downloaded IPSW file via iTunes.
All done