i can’t update 15.7 security I o s

You can't update your iPhone to iOS 15.7.6, sorry

iOS 12.5.7 is the latest iOS security update for iPhone 6.

Go to Settings -> General -> Software Update -> Download and Install (if you haven't already done that).

iPhone 6 can’t be update to a higher iOS (13 and later). 

If you have an outdated iPhone that cannot be updated to iOS 13 or later, many apps will not be able to download.

Outdated iPhone no longer meets the requirements for many apps.

Most apps require iOS 13.4 or later.                                

Considering a newer type of iPhone?

Read this before you buy a newer type iPhone.