Common question that is asked repeatedly. Short answer. Officially you cannot access the Dashboard from a remote computer.
Unofficially one can but it requires one to either use VPN or to use SSH and possibly modify the firmware to allow for remote Dashboard Access.
Here are just a few past threads to get you started:
http://community.wd.com/t/login-to-mycloud-dashboard-from-outside-the-network/93201
http://community.wd.com/t/how-to-access-dashboard-remotly-throgh-browser/147803
http://community.wd.com/t/access-dashboard-remotly-via-internet/94902
http://community.wd.com/t/configuring-remote-dashboard-access-can-it-be-done/92873
