Your Username and/or Password is managed through the User Settings menu which is accessed by clicking on the Gear icon in the top right corner of the screen. This menu contains all your account information in one easy to use location.
Click on the Gear icon will open the drop down menu where the User Settings page can be found. This page contains your account information that can be edited through the use of the Edit button located next to each entry.
The edit button will expand the menu selection and make each field visible for you to begin editing. If you wish to discard your changes, simply click on the cancel button located in the same location or your updates can be saved by selecting the update button at the bottom of that section.