How to update iphone 6 to IOS13?

Hello ~ Your iPhone 6 is not capable of being updated to iOS 13. If you need/require a higher version of iOS you will need a newer device. You can go to the black line at the top of this page and click on iPhone to see new choices.

Or:

Apple Store Online

Also if you decide to buy a second hand device…please read this first:

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

~Katana-San~

Not possible. you have to have an iPhone 6s or later. sorry, you're stuck on 12.