Switch between GDM and KDM

For those using the Ubuntu desktop as well as the Kubuntu desktop on the same machine, there exists an option to switch back and forth between the GDM and KDM window managers.

The procedure is simple:
Open a Terminal window, and type in the command:
sudo dpkg-reconfigure gdm

You'll be presented with two pop-up windows. The first pop-up explains a little about what GDM is, the second lists the available window managers – GDM and KDM.
Make your selection with the arrow keys and press 'enter'. That's it! When you reboot, the window manager will have changed to your selection.