You may not bring a lawsuit to change custody because you are a minor.  But your mother can bring a lawsuit against your father.   Have you spoken to her?   If you are being abused by your step mother and by your father you should speak to your mother, or to someone at school like a teacher, counselor or principal.   If you live in Arizona you or your mother can call the Child Protective Services Hot Line, 1-888-767-2445.  An investigation will be made.  If abuse is found they will place you with your mother.

When you step mother punched you was there a mark on your face or body?  If so, you should show it to an adult - your mother, an adult at school, or any other adult you trust.