One can attempt to roll back the firmware but doing so will open up potential security issues that later (or the latest) firmware has closed. Even then, rolling back may not guarantee the My Cloud Desktop program would continue to operate as before.
Performing a 4 second or 40 second reset via the reset button on the back of the My Cloud will only reset the My Cloud settings.
Performing one of the three Factory Reset options found in the My Cloud Dashboard > Settings > Utilities > System Factory Restore section does not change the current firmware to an earlier version. Depending on which Factory Restore option one chooses one may only reset the Dashboard options to factory default, or one could erase (or securely erase) all data on the drive and reset the Dashboard options back to default.
One could try one of the various unbrick methods to roll the firmware back to much earlier versions but doing so typically requires more knowledge in using Linux and or issuing various commands via Telnet or SSH. Generally a typical unbricking of a drive will erase all data on the drive.