To change your password after you have successfully logged in the first time, you will need to go to the "My Info" page.

To access this page, click on the drop down menu next to your name at the top right of the screen:

From inside the "My info" page, you can change any of the fields associated with your enrolment, including your email address, your password, or your time zone. 

When you are done, click "Update User" to save the changes.