To access your Profile and other platform settings, click on the Account Settings (small wrench icon) in the bottom left corner of your dashboard and choose Manage Profile.
If you wish, you can update your account info and even change your primary email address or account password.
This is also where you can change your sub-domain. This can be changed as many times as you want.
Let's move over to the Settings tab (also available from the main menu as Application Settings).
Sharing Networks for your videos can be enabled/disabled here (just click on each one you want). These are the networks that will show when you enable your sharing widget.