Help me!

Alright, I''ve tried going about this several ways, but none of them seem to work. I''m trying to log out my black_mage_s account, and keep the AnonymousPosterChild one as my standard. Now, the problem is, I can''t log out of the black_mage_s one. That wouldn''t be so bad normally, but this keeps me from changing my current stuff like signatures. Anyone able to help me?