Hi Cristina, Can i ask why you want to leave? You don't have to tell me of course but if things are not good for you then do you know anyone who can help you? If not then you can call childline, it is a helpline for children the number is 0800 1111 if you do need help.
You are allowed to leave and you do not need permission from your auntie. Do you think she would not be happy about it? It maybe be better to find a job before you leave as it might take you some time to find one. Good luck