How to update iOS on my iPhone 7 Plus?

An iPhone 6s, iPhone 6s Plus, iPhone 7, iPhone 7 Plus, or iPhone SE 1 isn't capable of 16 or above; they require an A11 or better CPU. To install 15.8.3, use a computer or the Software Update function in Settings.

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The most recent update for the iPhone 7 Plus is iOS 15.8.3

Update your iPhone or iPadApple SupportOfficial Apple Support › en-us

The iPhone 7 Plus cannot run iOS 16 or iOS 17, if that is what you are asking.