make up one's mind 是决定的意思，用法是make up one's mind to do sth.e.g:I made up my mind to give up going to college,我决定放弃上大学。 change one's mind是改变主意的意思。I changed my mind.我改变了我的主意。
前者是“某人决定，打定主意”，后者是“改变某人的注意” e.g:He made up his mind to teach in the rural area.他决定到农村教学。 He changed his mind not to teach in the rural area.他改变了到农村教学的主意。（意思是不去了）
