How to update software on Apple iPad?

That model isn't capable of 10 or above. To update it to 9.3.5, use a computer or the Software Update function in Settings.

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You have a first generation iPad Mini, which was release a decade ago (2012), will never be able to be updated past iOS 9.x.x. It is simply obsolete at this point, too old and lacks the hardware required to run any of the newer iOS versions. Time to retire that old device in favor of a newer, more modern iPad.