How to update iPhone 6?

Assuming you have a compatible device, see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

Hello,

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

Any equipment currently running iOS 12.5.7 can't be updated to anything higher.

An iPhone 5S, 6, or 6plus, will only update to iOS 12.5.7

This support article has instructions about updating an iPhone or iPad wirelessly --> Update your iPhone or iPad - Apple Support Read the article for recommended criteria for being able to use wireless updating.

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

If you want a video about doing this, follow this link —> https://www.youtube.com/watch/1FcE86kwODQ

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. If you want to run a higher system version than your current device is capable of running, you need to buy a newer device.

First of all, living160, no one can update your iPhone except you. However, in this case, even you cannot update your iPhone 6 Plus any higher. The hardware in your phone is not capable of updating.

If you mistakenly identified your iPhone as a 6 Plus, and you have a later model, you can try updating your iOS, by selecting Settings > General > Software Update. If your iPhone is eligible for an update, you will be prompted to do so.