Unable to update the iOS

Gwapakaayosikhyla wrote:

Update iOS to download the app that I want

The Related Article seems to indicate that you are interested in iOS 15.8.1.

What iPhone do you have? Is it one that is compatible with iOS 15? The iPhone 6 and 6 Plus, for instance, are not. If your iPhone is not compatible with iOS 15, it will not offer an update to iOS 15. If your iPhone is compatible both with iOS 15 and with something newer, it might offer you only something newer.

See also:

Update your iPhone or iPad - Apple Support

Updating iOS: common issues and solutions - Apple Community

What happens when you try?

Can you post a screenshot of the whole screen, it could reveal why you aren't able to update.

Make sure you:

• Are using a WiFi connection (not a hotspot).

• You have an active cell signal (You need both WiFi and cellular service to perform the upgrade).

• Are not using a VPN connection.

• Have your battery charged at least 50%. Better yet, keep it plugged in during the update.

• Do not have power save mode turned on.

• Do not have a beta version installed.

• You have at least 10 gigs of storage available.

Click on this link on what to do if you can't update your phone -

If your iPhone or iPad won't update – Apple Support (UK)