Need to update my phone but it won’t let me do I need to take it to AT

What happens when you try? Any error message? See if this helps: If you can't update or restore your iPhone or iPod touch - Apple Support

What happens when you go to Settings/General/Software Update?

And no, AT&T will be clueless. If you want to take it to anyone make a genius bar appointment. But we can probably resolve the problem here with some troubleshooting.

Go to Settings > General > About > Version If it shows iOS 15.7.1 you are up to date.