How do I update my iPhone 6 from iOS 12 to iOS 16?

Hello ~ You can update to iOS 12.5.7 but no further. If you need a higher version of iOS you will need a newer iPhone. Click below to shop for a new device…

iPhone - Apple Official Site

If you purchase a second hand device please take a moment to read these helpful links by clicking on below to make an informed decision…

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Also:

The All Too Common SAD Reality of Buying a Used iPad/iPhone

~Katana-San~

You don't update your iPhone 6 to iOS 16.

iOS 12 is the end of the line for the iPhone 6. No updates to iOS 13 or higher are available for that phone.