OTA failue is often not space free but bad dpkg dependancies. Uninstally to free space is quite possibly fixing those as weel as making space. Disabling repositories and rebooting will help.

In my case I read a post where somebody suggested uninstalling tuxrace and this let the app manager think it would work. I'd also symlinked /var/lib/dpkg/info to /home as it was apparently 16MB according to du. However this broke dpkg and the gui wouldn't install.

I worked this out as I used apt-get dist-upgrade which showed dpkg doesn't like cross filesystem links. Once I moved this back I had 60odd meg (I think this was du summing incorrectly as I didn't lose 16M of space) and ran dist-upgrade again. I saw my rootfs drop to 13MB at its lowest. I would suggest that 47MB is about the minimum, depending on what apps need to be replaced in place.

My deb cache is on /home, I did that ages ago, but seeing as the M5 update is 115MB or so it can't be using rootfs.

I realise after undoing the dpkg/info link and tixrace broken dependancy(?!), I probably would have been fine via the gui. But I love how dist-upgrade looks