I have a buster installation sitting around on my hard drive in dual
boot with beowulf.

I was planning to delete the buster, but I understand we still want to
test crossgrading from buster to beowulf.

So...

What is the current recommended way to crossgrade from buster to
beowulf (so I can test it properly)

And what logging would be useful to do while I do this?

In particular, is there any useful way to get a log during reboot to
the new system?

-- hendrik