Update is not available yet but i really want to update

The 6s has double the ram your 6 has so it works with the minimum requirement for iOS. Unless you were a tech wizard and can install more ram and trick the iOS then you have maxed out your limit with what you can put on it at this time.

if you want 13+ you need phone which supports the software

You will never be able to update your iPhone 6 Plus to iOS 13. The phone’s hardware cannot support iOS 13.

The iPhone 6 can not be upgraded beyond iOS 12.4.4.

No, they didn’t. If they updated they had a 6S Plus.