iOS 5 Direct Download and Install
Download the latest iOS 5 IPSW file directly from Apple server and install it using iTunes 10.5 to your iPhone, iPod Touch or iPad by following these steps:
1. Download the iOS 5 for your device.
2. Connect your iPhone (iOS devise) to your computer.
3. When iTunes opens, select your iPhone under Devices in the Source List on the left.
4. OPTION-click (on Macs) or SHIFT-click (on Windows) on the Update button in iTunes.
5. Now you will be able to tell iTunes to use the IPSW file you downloaded to update your iPhone, iPod Touch, iPad.