My iPhone iOS is up to date but I need iOS 16

If it isn’t an iPhone 8 or later or an SE 2nd or 3rd Edition then 15.7.1 is the latest version available. If your phone is eligible delete the beta profile that you installed when you joined the beta program.

If it's stuck on exactly 15.7, open Settings, go into VPN & Device Management, remove the beta profile, restart the unit, and run Software Update again.

If it's an iPhone 8, second generation iPhone SE, or newer, look for an option to upgrade it or see above.

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Can you tell us what model name of iPhone that you have please?

Settings > General > About > Model Name

This worked for both my iPhone and my iPad. Thank you.