These instructions are for Ubuntu 12.04 running the Unity desktop on which the Lubuntu Core Desktop was installed using either the Ubuntu Software Center or sudo apt-get on the command line.

The instructions may be the same for other versions of Ubuntu, but no guarantee is made.

When the Lubuntu Core Desktop is installed in Ubuntu 12.04, it installs several packages and libraries it requires as well as some optional packages. Not all these packages and libraries are uninstalled when you uninstall Lubuntu Core Desktop. Several packages (like galculator) do not get uninstalled.

Quick Uninstall

This is not recommended because it will remove all packages normally installed with Lubuntu Core Desktop. This may include packages you previously installed (such as galculator) or that were installed as dependencies for other packages.

Note: this uninstall command assumes Lubuntu Core Desktop was installed on a fresh Ubuntu 12.04.

1) Open a terminal (instructions can be found here).

2) Enter the following command (it is very long and a single line):

sudo apt-get remove --auto-remove --purge  elementary-icon-theme galculator giblib1 gnome-icon-theme-full libfm-data libfm-gtk-data libfm-gtk1 libfm1 libgif4 libglade2-0 libid3tag0 libimlib2 libjpeg-progs libjpeg-turbo-progs libmenu-cache1 libobrender27 libobt0 lightdm-gtk-greeter lubuntu-artwork lubuntu-artwork-12-04 lubuntu-core lubuntu-default-settings lubuntu-icon-theme lxmenu-data lxpanel lxsession lxshortcut miscfiles obconf openbox openbox-themes pcmanfm plymouth-theme-lubuntu-logo plymouth-theme-lubuntu-text scrot xscreensaver xscreensaver-data

It is easiest to copy the line and paste it into the terminal (right-click on the terminal and select Paste from the popup menu).

Preferred Uninstall

The better way to uninstall it is to follow the directions on this page.

This will show you on how to uninstall only the packages that were installed when Lubuntu Core Desktop was installed. The instructions are generic and work for any installed package.

It involves:

identifying which packages were installed and
creating a command to uninstall only those packages

It leaves intact any packages you may have installed (like galculator) or that were installed as dependencies for other programs instead of blindly assuming that they were installed along with Lubuntu Core Desktop.