This is applicable in situations where you have created multiple directories in your subscription. For example, I have 4 directories as shown here:
In this case, I want to change the directory associated with my subscription to the rickrainey.com directory because I’ve associated my domain with that directory.
To do this, click on the Settings tab (left of screen) and then the Subscriptions link (top of screen).
Click on the Edit Directory link in the task bar (bottom of screen).
Change the directory field to the directory you want to default to.