Fences 6 is successful installed. Before running the suggested purge routine I tried out installing Fences 6 installation procedure without following the hint first to stop Fences 4 before continuing the installation routine.
In German language

Translated text in turn: This program will deinstall Fences 4. If Fences 4 runs right now than shutdown it please, before you continue the deinstallation process. Else click on continue (weiter).
That's why I tried to continue the deinstallation process on the basis of an inactive Fences 4, aborted the deinstallation process and found no solution to deinstall Fences 4 with an inactive Fences 4.
Today I didn't abort the deinstallation but clicked on continue and all run without any problems. Even my window layout was saved corresponding to the unchecked checkbox to remove the settings. In my opinion this phrase has confused me. Because my experience is to follow the given hints to avoid further problems.
That's very much for your support.