I want to appdate my iphone

Assuming you're trying to update your device wirelessly (via wifi), see this suppport article:--> If your iPhone, iPad or iPod touch won’t update

If the issue persists, try to update it via computer:

Learn how to update your device manually if you're using a Mac with macOS Catalina or later, or if you're using a Mac with macOS Mojave or earlier or a Windows PC.

If you still get no help, contact Apple Support directly, using this link:--> Get Support

Regards

Giulio

Force restart your iPhone.

What happens when you try?

How are you trying to update your iPhone?

What model do you own?

With what iOS version?

Okay.

Erase your iPhone or force restart your iPhone.

Try doing that.