How do i change my avatar's name?

my sister found my email password and decided it would be funny to create a male avatar named Michel and run around on yahoo answers pissing people off. im not kidding, she wrote some pretty bad stuff, my "blocked list is so big, and im surprised my account is still running -.- anyway, i decided to keep the avatar, change the gender and whatever, but now i want to change the name, and i dont know how.