After looking before and following the instructions there, I've
upgraded Debian wheezy to Debian Jessie and apparently that isn't
how you do it now.

So what am I supposed to do now?
I'm looking for a set of migration steps that don't involve blowing
stuff away and loading an iso.

On a side question, how do you permanently lock a Debian:Jessie system
to boot the system-init(?) boot up. I had a look but my old knowledge
of editing grub.conf doesn't appear to apply.

T.I.A