Comment 3 for bug 264282

as i pretty much expected do-release-upgrade -d failed as well:

Not enough free disk space

The upgrade aborts now. The upgrade needs a total of 151M free space
on disk '/boot'. Please free at least an additional 53.9M of disk
space on '/boot'. Empty your trash and remove temporary packages of
former installations using 'sudo apt-get clean'.

but it seemed worth a try to confirm