Hello, deni09.
Thank you for using Apple Support Communities.
Take a look at some of these steps in this article: If your iPhone, iPad or iPod touch won’t update
"Try updating your device again using the same network. If you still see one of these messages, try updating your device using another network or update your device with your computer. If the issue happens again after trying to update with multiple networks, remove the update.
Learn more about iOS and iPadOS updates."
If you're still getting stuck on updating, you may need to update using a computer. Do you have a computer with iTunes or Finder? If not, a friend or family member's computer would work too. If you have access to a computer, follow the steps in this article to update your iPhone:
Update your iPhone, iPad, or iPod touch with the Finder
Update your iPhone, iPad, or iPod touch with iTunes
If neither of those are an option, perhaps a local service center may help. You can use this link to find a nearby service center: Find Locations
Cheers!