Upgrading HDD

My Cloud OS 3 Personal & Network Attached Storage My Cloud
3

Given that such an upgrade is essentially the same as unbricking a a 4TB device using a 2TB device image, I think this thread should tell you what you need to know:

http://community.wd.com/t5/WD-My-Cloud/GUIDE-How-To-Unbrick-your-2TB-3TB-4TB-My-Cloud/td-p/765959