How to change attitude?? A get more mature?

I'm a very Bi- polar person. I'm either very mad or really happy. I don't know how to change this??? I get mad when they tell me things. I get mad easily. I cry a lot when I get mad. I don't act my age sometimes. I'm 19 and when I get mad I act like a 6 year old. I'm not mature when it comes to truth, handling situation and being critized. It's like I just want to hear good things and I can't handle the truth. I don't know what to do. I get mad at my mom often. and she tell me to change and get mature but I don't know how??? What's the first step???