How do I upgrade my iPhone version

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. 

An iPhone 6s, iPhone 7, or iPhone SE 1 isn't capable of 16 or above; they require an A11 or better CPU. To install 15.7.6, use a computer or the Software Update function in Settings.

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