My parents are to controlling. They picked my classes, cause they want me to go to law school, but I am not the type of person who can sit behind a desk all day. I want to be in MMA as a job. But they won't even let me train with the local gym. How should I tell them to back off?

Well, have you tried talking to them about what you want to do?
I don't mean just like "I want to be in control, stop picking my classes!", but actually sitting down, and having a mature conversation with them.

I strongly recommend you do that.
When you HAVE done it, how did they react? How did you tell them? Did you become hostile if they wouldn't listen to you?

I going to be hard standing up to them my mom is the same way but just say I want to do something else with my life. I know I'm not going to be happy doing that. I know your trying to help but I want to make the decision for my future. If I make a mistake and I'm not happy I can always do that later in my future. Hope this helps.

You can tell them what you want, back off or whatever, but they will probably hold the purse strings over you meaning if you choose to do what you want they may not be willing to pay for your schooling.

When your having your tea say "look mom and dad.I'm really sorry but I have to live my own life. I want to be what I want to be and I want to be a MMA. I really hope you understand because i'll have to make my own choices when your gone. I think I should start now don't you?"