Okay i need some help...

there are four accounts on my compy see
My Moms
My Dads
Mine
My Bros

My bro took over my comp by setting passwords for my parents accounts (and he didnt tell them what they were) and setting mine and his to limited accounts so i cant change it unless he tells my parents the passwords to change it.

BUT! here is my query: anyway to change it through Command Prompt?

Help would be... helpful PLZ I NEED HELP!