When you take your mouse over the right navigation pane, in the upper-right corner you get two options: Profile and Logout. If you click on Logout, you will return back to the login screen.
On the other hand, if you click on Profile, your user profile page will open up.
This profile page reflects the profile information of the currently logged-in user. The administrator can manage other user accounts at Administration > Access Control > Users tab.
For an account, the email address is treated as the "username." Once you sign up with it, you cannot change it later.