How to update my iPhone 6 in latest version iOS 13

You can post that screenshot as many times as you like, it's still not going to change the fact that an iPhone 6 can't be upgraded beyond 12.5.5.

If you have apps that need to run on a newer OS, you will have to buy a newer phone

Maa1992 wrote:

Why I buy newer phone ?

Why you don’t launch latest iOS version support every I Phone ?

First “you” is meaningless in this user to user forum; no one here has any say in how Apple does anything.

Products go out of date and become obsolete; for example, my IBM XT PC from 1983 can’t run Windows. And a 7+ year old iPhone 6 doesn’t have enough RAM to run newer versions of iOS. If you had an only 6 year old iPhone 6S it could run iOS 15, but 7 years was the cutoff for upgradeability.

The iPhone 6 is not compatible with iOS 13 or higher.

Then you need to get a newer phone that can run the newer iOS.