How to doing iPhone update?

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The iPhone 6 Plus can only be updated to iOS 12.5.6.

The iPhone 6 Plus cannot be updated to iOS 15 or iOS 16.

Your profile shows that you have an iPhone 6 Plus. That device will not update any higher than iOS 12.5.6. It does not have the capacity to run anything higher. If you need a higher iOS, you will need to purchase a newer iPhone.