Software update iOS 15.4.1

You might get very old if you're trying to update an iPhone (from iOS v12.4.1 to v15.4.1) over the air/wirelessly, and most likely you won't be able to do it.

In such a situation, I suggest that you update that device via computer (if you don't have a computer borrow one from your friends/neighbors, or ask for help at an Apple Store or Authorized Service Provider), then 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.

Regards

Giulio

My pleasure, Cat.

Yes, on a Mac running BigSur or later you'll use Finder to update the iPhone.

Best of luck

Giulio