Works a little different on my DNA. Go to apps, select all apps, scroll to MAIL, tap on app, when it opens select, CLEAR DATA, you'll get warning that your about to delete all data, continue. When I did all this then opened the MAIL app, Aqua mail was not on the list so I closed it and opened Aqua mail. Aqua mail was now my default email program. My guess is when I cleared data in the Reg mail app, since Aqua mail was already installed, it became my default email.
