How do I update my iPad mini 2?

If your iPad has been stuck on iOS 9.3.5 for the past few years, with no upgrades/updates forthcoming, then you

own an iPad Mini 1st generation, NOT an iPad Mini 2.

A 1st gen iPad Mini cannot be upgraded beyond iOS 9.3.5/9.3.6.

Its internal hardware is too old, underpowered and completely incompatible with any current and future versions of iOS.

Sorry.

If you need an iPad that can run the latest and greatest versions of iOS, as well as, the most current apps available, then, you will need to purchase a new iPad from Apple or a discounted, refurbished iPad from Apple’s Refurbished & Clearance section of Apple’s Website.

Best of Luck to You!

This would indicate that you have an iPad Mini 1

Please verily the model number at Settings - General - About - Model = ???