From FCKeditor Docs

DeleteFolder

Deletes a folder.

Sample Request

Deletes the folder /Test/, of the resource type “Files”.

connector.php?command=DeleteFolder&type=Files&currentFolder=%2FTest%2F

Note that “currentFolder” contains the complete path of the folder.

Sample Response

<?xml version="1.0" encoding="utf-8"?>
<Connector resourceType="Files">
 <Error number="0" />
 <CurrentFolder path="/Test/" url="/userfiles/files/Test/" acl="255" />
</Connector>

Note that the folder path may contain non ASC-II chars.