Software version 12.5.7

Hello ~ You can update to iOS 12.5.7 but no further. Click on the links below….

Update your iPhone or iPad - Apple Support

If your iPhone or iPad won't update - Apple Support

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~

An iPhone 6 cannot update beyond iOs 12.5.7. That is the most current version it supports. It lacks the hardware, RAM and CPU to run anything newer.

Asking for a newer version, is not going to make the hardware capable of running it.

You will need to buy a newer device, if you need a newer iOS version.

Please read the reply above.