Not sure if this helps:
From here -
To delete a shared folder, select the folder checkbox and click “Remove”. You can select the option “Also delete the data. (Mounted ISO image files will not be deleted)” to delete the folder and the files in it. If you select not to delete the folder data, the data will be retained in the NAS. You can create a shared folder of the same name again to access the data.
Previous link was for version 4.0, this is for version 4.2, but it looks about the same procedure in case there are subtle changes from my last link.