Video to explain :How to upgrade to iOS 5 for iPhone 4,3GS ,iPod touch 4G, 3G and iPad 1, 2

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How to upgrade to iOS 5 for iPhone 4,3GS ,iPod touch 4G, 3G and iPad 1, 2:
1: Download the iOS 5 IPSW file for iPhone 4 and iTunes 10.5 - Click Here.
2: Install iTunes from the downloaded DMG file.
3: Update your phone with itunes by connecting it and clicking on the "Check for Update" button while holding down the Option key (Shift on a PC). Select the iOS5 IPSW you just downloaded and confirm.

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How to Activate iOS 5 without developer account
1: Triple click the home button to activate Voice Over
2: Triple click the home button and Emergency Call will appear.
3: Click on Emergency Call and, while it's switching, swipe with your three fingers down.
4: The Notification Center will appear!
5: Click on the Weather widget and wait for the weather app to load.
6: Click on the home button to exit to the iPhone's springboard.