Pls update my iPhone 6 to iOS latest version

To update to the maximum of iOS 12.5.7, please see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

Aup date

This is not possible the iPhone 6 is too old to update to any iOS version further then iOS 12.5.7