Teste isso:
Abra um terminal
Pressione Ctrl + Alt + T
Execute:
sudo -i
apt-get update
apt-get install --reinstall aptitude deborphan
aptitude remove '?and(?reverse-depends(lubuntu),?not(?reverse-depends(?exact-name(kubuntu-desktop))))'
aptitude remove '?and(?reverse-depends(lxde),?not(?reverse-depends(?exact-name(kubuntu-desktop))))'
apt-get install --reinstall kubuntu-desktop
deborphan
apt-get --purge remove $(deborphan)
deborphan --libdevel
apt-get --purge remove $(deborphan --libdevel)
deborphan --find-config
dpkg --purge $(deborphan --find-config)
apt-get autoremove
apt-get clean
reboot
Isso remove os pacotes instalados que dependem da versão reversa do lubuntu e não os do kubuntu-desktop.