How to replace lubuntu for ubuntu desktop ?
Solution 1:
I'm not sure but if you do this you'll be able to retrieve Ubuntu (under a textual console not from a graphical terminal):
sudo apt-get install --reinstall ubuntu-desktop
sudo apt-get autoremove --purge lubuntu-desktop
The first line will force to re-install Ubuntu desktop and the second one will remove Lubuntu desktop. After reboot you'll be good.