I want to update my iPhone

Go to setting > General > Software update and follow the instructions on the screen keep your iphone in charge while updating, or connect to iTunes or a Mac and update from there

iPhone models compatible with iOS 15.5

iPhone models compatible with iOS 15.5 - Apple Support

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 15.8, use a computer or the Software Update function in Settings.

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