How do you go about filing a legal malpractice suit against a lawyer?

My husband's former lawyer was completely unprofessional. He failed to show up to court on numerous occassions. He made many promises that he did not fulfill. He would say that he was doing all of these different thing for the case, but nothing was ever done. Failed to answer or return phone calls even in medical emergencies while my husband was incarcerated. He never went up to see his client, his business phone got disconnected and he never answered any calls. After months of waiting and not hearing anything from him we hired a new lawyer. The new lawyer attempted to get in touch with him to get any files, he didn't get back to him for 2 weeks and when he did talk to him he told him he would meet up with him to give him the files, but then never answered his call. There are many more ex