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Yes. Plug into iTunes and select update and it will update your iOS to the latest version
Will work for the 1st gen iPad?
Sent from my iPhone 4 using Tapatalk
Yes. Regardless of what iDevice you have, iTunes will only update it to the latest iOS that the device can run.
iOS 5.1.1 was the last update for the original iPad.
Sent from my iPhone or iPad mini