You are not allowed to change your username, but you can change your email address. To do the same you need to visit the settings tab in the menu above –

Screen Shot 2013-05-17 at 10.56.38 AM.png

The next screen would give you an option to change your email address. (As shown below)

 

Screen Shot 2013-05-17 at 10.59.59 AM.png


Once this is done and the changes are saved, the new email address would be used for all communication in the future.