I can't update my iPhone 6s

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 an 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 can't go any higher) 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.

- An iPhone 6S through 7, or SE(gen. 1), can currently only update to iOS 15.7.5

If your Apple mobile device won't update, read this support article --> If your iPhone or iPad won't update - Apple Support

Another, less common reason for not being able to update is if you were using a beta version of software. Refer to How to uninstall iOS or iPadOS beta software - Apple Support

Do you have an iPhone 6s....or....do you have an iPhone 6?

Not sure? Check Settings > General > About > Model Name