I want to be an actress, any tips?

I'm currently 15, I'm a female and my biggest dream is to be an actress. But the problem is.. I don't know where to start. And another problem is... I have an Australian accent but my top ambition is to star in Hollywood movies. My aunty is in contact with someone who is an agent for commercials, do you think I should get try out for casting? Will it help me? Also should I do Drama for my final exams in High School? And what should I do about my accent? I want to learn how to speak with an American one but no matter how hard I practice it sounds so fake! And one last thing.. I'm shy. Yes, I know, how stupid of me. But I have anxiety and it takes me a lot of effort to get over my worries. But I will find a way to do so, any tips regarding confidence though? Also I'm tall and skinny and many have said I should be a model. Would getting into modeling help my chances? I plan to move to LA or Vancouver in the future to help me get known out there & find a good agent after doing a course for Drama at university in Australia.