To uninstall xmonad just follow these instructions.
sudo apt-get remove xmonad
This will remove just the xmonad package itself.
sudo apt-get remove --auto-remove xmonad
This will remove the xmonad package and any other dependant packages which are no longer needed.
If you also want to delete your local/config files for xmonad then this will work.
sudo apt-get purge xmonad
Or similarly, like this xmonad
sudo apt-get purge --auto-remove xmonad
|Maintainer||Debian Haskell Group <firstname.lastname@example.org>|
|Description||Lightweight X11 window manager written in Haskell Haskell. Windows are managed using automatic layout algorithms, which can be dynamically reconfigured. At any time windows are arranged so as to maximise the use of screen real estate. All features of the window manager are accessible purely from the keyboard: a mouse is entirely optional. Xmonad is configured in Haskell, and custom layout algorithms may be implemented by the user in config files. A principle of Xmonad is predictability: the user should know in advance precisely the window arrangement that will result from any action.|