Hi im 13 and i want to go live with my grandma but my mom wont let me how can she get custody of me ?

I'm sorry to hear that you're frustrated with your current living situation. I probably don't have to say this, but it's difficult being a teenager sometimes. The courts do not allow third parties (which would be your grandma in this situation) to bring a unilateral action (meaning on their own) for custody. A third party may seek custody from the court if it is part of an ongoing custody proceeding involving your mother. There are possibly other avenues but they are much too complicated to discuss in a forum such as this. My advice is try to get along with your mother. It might be difficult at times and you may not agree with her but your situation may improve if you try to get along with her. Good luck and I hope this helps.