how to do iOS 12.5.7 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~

Sorry, but that is not possible. Any device running iOS 12.5.7, can not be updated further.