Install the add-on Enable Root SSH Access. Connect to the NAS using Putty or any other SSH client with the user name "root" and the same password as the admin user of the control panel. The user homes are located in /c/homes
and the shares are under /c
. In my case, this did the trick:
mv /c/homes/tomas/Series /c/Public/Series
And voilà, one terabyte of video moved to a different share in under 5 minutes (including the time it took to install the add-on and restart the NAS.)