My iPhone 6 need update

Hello,

There are different ways to ensure the highest iOS that your device will support is installed on your device.

This support article has instructions about updating your iPhone or iPad wirelessly --> Update your iPhone or iPad - Apple Support

You can also use Mac and PC computers to update system software: Update iOS on iPhone - Apple Support

When updating, your device will update to the highest version currently available that it will support, or it will just say it is up to date and won't install anything. Apple indicates ( Unable to update my iPhone 6 Plus from 12… - Apple Community ) I need to point out the obvious and state that if you want to run a higher system version than your current device will run, that you need to buy a newer device.

- If you have an iPhone 5S, 6 or 6plus, the highest you can currently update to is 12.5.7

- If you have an iPhone 6S through 7, or SE(gen. 1), you can currently update to 15.7.3

What are you trying to update to?

That device can’t run iOS 13, 14, 15, or 16. 12.5.7 is as far as it can go.