Can't update iPhone 5S to the last iOS version (Verifying update)
Restore is sometimes needed from iTunes when an over the air (OTA) update fails you repeatedly. iTunes restores have a couple of other advantages in addition to being far more reliable:


chance to back up locally instead of iCloud
less free space needed on the device (you don't need space to stage the upgrade and contain a download all on the device - just space needed to apply the change)