I don't know much, but I know it can happen. A 2nd year student I know is transferring to an MD school in his home state, mainly because of family hardship. YOu have to have a really good reason in order for your school to let you go without a fight. Schools do not like to lose students.
It is hard but it can be done. From what I hear, it is easiest to do between 2nd and 3rd years, though.
Best of luck