You would need to file a Petition for Guardianship to allow your sister to have legal guardianship over you. Will your parents consent to the guardianship? If so, that will make things easier.
The information provided is not intended to create an attorney-client relationship. You are not to rely solely on my answers, but should instead contact an attorney and provide them with the details of your matter. S/he will be able to provide you with more complete advice. If you have more specific questions, feel free to contact me.
Essentially, you can't do this on your own. Your sister would have to file a Petition for "Guardianship, and your parents, if living, would either have to join and consent or be served with a summons and given the opportunity to object.
Another solution might be for you to file a Petition for Emancipation, which would make you a legal adult in Mississippi--but again your parents would have to join and consent or be served as above. You might want to check with the school to see how an emancipation would affect your eligibility for financial aid.
You will probably need to hire a lawyer to assist you with either option.
Answers provided are for informational purposes only. No attorney-client relationship is intended or implied.
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