I inquired with LL and this is the answer I got from LL directly:
"Thank you for your inquiry. Unfortunately, User Names are not changeable. Instead, you can simply re-register for a new User Name and Password, then notify LL and LL will de-activate the previous account. If you have any other questions or concerns, please don't hesitate to contact us US toll free (888) 297-3299 or from outside the US at (310) 215-8060."