Seriously? "Re-running migration to V14 is NOT-SAFE and SHOULD NOT be attempted."

Hello again.

I am trying to do as you say but I am unable to find instructions for migrating a V13 installation to V14. All the posts I have found here say that restoring a V13 data backup to a V14 instance is the least problematic way to do it.

Would you point out the correct instructions to me please?

update
Trying: