Put iOS on your iPhone
How to put iOS to your iPhone
[Re-Titled by Moderator]
iPhone 6, iOS 12
Question marked as
Hello,
There are different ways to ensure the highest iOS that your device will support is installed on your device. For an iPhone 6 that will only be iOS 12.5.7.
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 offer to install anything. If you want to run a higher system version than your current device will support, you need to buy a newer device.