How do I deal with my severe anger issues?

I am 13 and have the worst temper anyone of my friends or family has ever seen. I have been compared to the girl from the exorcist. I am very destructive when I am mad and have thrown things heavier than me (121 lbs.) across the room purely out of adrenalin. I have even hurt my self in doing so. I am worse than the girls from the bad girls club. I have threatened to kill people and meant it before. I can hold grudges for a very long time, up to 6 years. And I don't forget. How do I deal with these issues so I don't kill someone?