How to update iOS 12.7 to iOS 16

An iPhone 6 plus can't be updated beyond 12.5.7, it doesn't have the hardware needed to run anything higher.

If you need a higher iOS version, you will have to purchase a newer phone.

To update to 12.5.7 -

Go to Settings > General > Software Update.

This link will show you how to update your iPhone, iPad, or iPod touch using WiFi -

Update your iPhone or iPad - Apple Support Update your iPhone or iPad - Apple Support

This link will show you how to update using your computer -

Update iOS on iPhone - Apple Support Update iOS on iPhone - Apple Support

It's not possible. iOS 12.5.7 is the end of the road for the iPhone 6. No more updates.

To run iOS 16, you will need an iPhone 8 or higher.

No.

How to update iphone 6 to ios 16

You don't, if you would read through this post, the answer has been given.

No update for the iPhone 6.

You need an iPhone 8 to run iOS 16.