
The steps are as follows:
1. Install kde-window-manager (I used Synaptic). This will install a lot of kde-packages.
2. Open the following file as root:
sudo nano /etc/xdg/xfce4/xfconf/xfce-perchannel-xml/xfce4-session.xml
Search for the following line:
<value type="String" value="Xfwm4"/>
Change it to:
<value type="String" value="Kwin"/>
3. To run kwin each time on startup, add an entry to crontab: crontab -e
Add a line: @reboot kwin --replace
4. Restart the computer. It should run with kde window manager now.
5. Using the kde window manager will disable the workspaces in XFCE. To add workspaces, press CTRL + F8 and click on +.
6. To change the window manager's settings, click on a window's title with the right mouse button. Go to more actions > window manager settings