According to the FAQs page, there is no way: http://www.stanford.edu/group/pandegroup/folding/faq.html#stats
Statistics, teams, usernames
How can I change my username?
The simplest way to change your username is go to the configuration panel (right click in the graphical display or click on the sys tray icon). You can change your username at any time. However, old work units will remain credited to the old username.