See here: http://forums.demigodthegame.com/354866 That should help 
I never changed my name so I'm not 100% sure on how that guy changed it in the first place, but if you change your Impulse login to use your email instead of user name it should always work even if you change names.
You can either change back to your old name to patch then change to the new one again, try to do what that guy did in his last reply, or try to use the email to log in (click the Impulse log on the top left and do change login).