Hello there @BSarmady!
I would suggest to never touch registry values unless you are absolutely sure of what’s being changed. Checking around the community, the most straight forward way to disable Zen is from the BaseEngine.ini file, as seen in the following thread (just avoid the zenserver.exe step):
After that, change the environment variable to a local drive hard drive location, as seen here:
As for the disk space issue, clear the contents from AppData\Local\UnrealEngine\Common\Zen after disabling Zen. You can also delete DerivedDataCache contens from both project and engine directories.