How do i change my legal guardian?

I am 16, and I am currently living with my aunt and uncle. My aunt is my dads sister. Both of my parents are deceased. I am very unhappy, my aunt and uncle recieve checks amounting to the sum of $1152 a month and theyve been collecting this for the past 40 months. There is less than $100 in my bank account, and there is none put aside for college, and none put aside for my vehicle which still isn't fixed. I work, work, and work again, All i ever seem to do with my time is keep up excellent grades, A's, with a few B's, and I clean all of the time. Whenever I ask for new jeans or something she tells me to use my own money... WHAT MONEY? I dont have any, she doesn't give me anything except 10 dollars for lunch each week. When my parents divorced in 2000 I chose to live with my dad which was the wrong choice, i left my mom alone, and it turns out she was in the last years of her life. In 2006 when my dad was killed, I chose to live with my aunt instead of my gma who was always there for me. My mom died 2 months later, and then my brother died a year later. I have done nothing but put up with heartache. I find my current living situation difficult because my aunt doesn't trust me, and I dont trust her. Im literally the step daughter, the cinderella story all over again. She went through my drawers last night, looking for my underwear, because I wasn't wearing any earlier that day. She tells me that I need to wear them although I find them uncomfortable. I was sent to the grocery store to pick up some items, I come back and she confronts me and says that "shes been watching my panty line for quite sometime and the fact that I dont wear underwear started 3 years ago isn't true." .... It is true. This is just one little thing that she made a huge problem. I only recently started going to peoples houses, and they only let me go for a night and i have to be home mid day. Its not fair at all to me since I work all the time. I want a break. I cant take living in this household any longer, I want to live with my grandmother, how do I do so?