After unzipping the file to get to your *.DEB version you have to rename that version. So lets say you are on 3.3.02.165 and you want to go back to 03.03.01.156, do the following.
1. Download gpl-source-wd_my_cloud-03.03.01-156.zip
2. Unpack the zip file to the *.DEB file.
3. Rename the *.DEB file to a version number that is highr than the version you are on. Example: rename 03.03.01.156 to 3.3.02.166 to replace 3.3.02.165.
4. Go to your Dashboard and do a manual firmware update. This will restore the older firmware.
BEWARE: that any scripts/functions that have been changed with the firmware you are on and are not addressed with the older firmware are still the current version's script. I would do this as a last resort in trying to find a fix elsewhere on the forum.