I want to rollback OS 5 to OS 3

This is my problem trying to go back to OS3:

root@WDMyCloud ~ # dd if=/dev/zero of=/dev/mtdblock1
dd: writing ‘/dev/mtdblock1’: No space left on device
509113+0 records in
509112+0 records out
260665344 bytes (248.6MB) copied, 2.872580 seconds, 86.5MB/s

I want the hdd to go to sleep

I followed Instructions, but now i stuck in safemode.
Cant upload the firmware. Endless circle rotating.
Is there any solution for this Problem meanwhile?

is this step not delete all my files/data inside?