What is the best way to have my son come back and live with me?

My son wants to come back and live with me. Several years ago his father took me to court to get custody. They asked my son where he wanted to live and he choose his dad. My son has realized that he has made a bad decision. His father is never there. My son comes home from school and his dad leaves for work around 3pm and does not return until 3am. He is staying home alone this whole time. No help with homework, no one to make him dinner. This is completely ridiculous in my eyes. My son is raising himself. His grades in school are just barley passing. I really want to do something but I don't have a lot of money for a lawyer. I had thought of just calling child protective services and having the go out there when his dad is not home but I don't want to make the situation worse than it already is. My son will be turning 14 this month and I had read somewhere that he could choose who he wanted to live with. Can he do that even though we have court docs with his dad having custody?