How can I update my iPhone 6 to iOS 14

You can't, the iPhone 6 does not have sufficient RAM to run iOS 13 or later and you cannot add RAM.

No, 12.5.6 is as high as it will go. You need a newer phone to update, I would suggest you get at least an iPhone 8 so you can run iOS 16.

See my last post.

Settings > General > Software Update