Switching between Kubuntu and Ubuntu without re-installation

To have both installed, you can install ubuntu-dekstop for Gnome-based ubuntu, and kubuntu-desktop for Kubuntu.

If you have both installed, you can configure the default display manager with

sudo dpkg-reconfigure gdm    (or kdm)

Either way you can choose whether to use Gnome or KDE at the login screen.

To remove one, you can uninstall ubuntu-desktop or kubuntu-desktop, then run

sudo apt-get autoremove

Depending on any additional packages you installed, some dangling packages may remain.

If you have a separate home partition, you can just reinstall Ubuntu/Kubuntu, formatting your root partition, without touching anything in your home partition. This will give you a clean installation, except for some config files remaining in your home partition. Of course, still make sure you have a backup of your important data.

sudo apt-get autoremove

will not work as stated above . You have to find out the whole list of dependencies from the meta-package 'kubuntu-desktop'

Look at https://help.ubuntu.com/community/PureGnome