Why my phone can’t update version 15.5?

Hello rotana80,

There are a couple of different ways to update your iPhone. You can find them here: Update your iPhone, iPad, or iPod touch - Apple Support

Be sure to follow the instructions on how to make a backup of your data before updating.

If you continue have any issues, work through the steps outlined here: If your iPhone, iPad, or iPod touch won't update - Apple Support

Have a good day.