How do I get the money my grandfather left me in his will?

My grandfather had a retirement account with Alcoa. He worked there until he retired. That was back before 401 K. He put money into his retirement account and Alcoa matched it. Then they set the money aside in an account that drew interest so that when he retired he would draw the interest from the account and that would be his retirement. He was allowed to leave the account to an immediate family member. He left the money to me and my family had it put in their name because they told the judge I am mentally ill and too crazy to spend the money on rent and groceries and they need to manage the money for me. However, I do not get a penny of the money. They keep it and spend it on themselves. Plus, I am perfectly capable of paying rent and buying groceries. I have been doing just that since I was eighteen years old without any help from my family. I get disability for being pschyso-effective. I am mentally ill, not incompetent.