ipad one

If you have an original iPad, as your post's title suggests, the highest iOS version it can ever have is iOS 5.1.1.

If you have a later iPad, it cannot be updated to iOS 8 either. If you update it, it must be updated to the current iOS which is iOS 9.2.1.

A first generation iPad can’t be updated past 5.1.1.

(139324)

The first generation iPad can only go up to iOS 5.1.1