Instructions are pretty clear but I get really nervous when I run the upgrade command and the first window I get is the dreadfull initial setup warning that going forward will wipe out everything on the box and apache and do its thing.
Is it safe to do this? That box is main dns for a lot of live domains right now I would hate to loose them because of a bad upgrade.
There is no upgrade in place approach available/tested.
Maybe wait until more people have reported their success and/or any fixes for the upgrade before embarking on the above. MIAB v57 on Ubuntu 18.04 is good for some months yet.