How to update 5.1.1 iOS to 9 IOS

Depending on the model of iPad you have you may not be able to update to iOS 9.

What model of iPad do you have? Does it have a camera? If it does not have a camera, its a first generation iPad and cannot be updated beyond iOS 5.1.1

Identify your iPad model - Apple Support

If you’re using a first generation iPad, you can’t. Otherwise, use the Software Update function or update it from iTunes on a computer.

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If settings, general, software update says it is up to date, then it is up to date. The update system will only ever offer you the most recent iOS release compatible with your hardware.