How do I update iOS on my iPhone ?

An iPhone 5s, iPhone 6, or iPhone 6 Plus isn't capable of 13 or above; they require at least 2GB of RAM. To install 12.5.7, use a computer or the Software Update function in Settings.

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If you still have the iPhone 5s listed in your profile........updates for this phone ended long ago.

Tap Settings > General > Software Update to confirm.