How to update my iphone 6

To update to the maximum of iOS 12.5.7, please see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

It's not capable of 13 or above. To install 12.5.7, use a computer or the Software Update function in Settings.

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