I can't download iOS 15 on my iPhone 7 Plus

Cremer12 wrote:

After downloading the iOS 15 it will ask get the iOS 14

Most likely you have an iOS 14 beta on your phone. You will have to remove the beta. And think twice before installing a beta next time→How to uninstall iOS beta software - Apple Support

If the usual update is not working, then try using a computer, as is described here:

Update your iPhone, iPad, or iPod touch - Apple Support

The only available option will be iOS 15.5.

What happens when you attempt to update?

Any error messages?

What is the existing version of iOS?

Please provide a screenshot of the error message.