How do I update my iOS

If you're referring to the iPhone 5 below your post, it's not capable of 11 or above.

If you're referring to an unit on 14.0, use a computer or the Software Update function in Settings; if you encounter a specific issue, describe it in this thread.

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If your phone is not yet running the most recent version of iOS with which it it compatible, see:

Update your iPhone or iPad - Apple Support

Updating iOS: common issues and solutions – Apple Community

Then you use the Software Update function in the iPhone's Settings.