Alabama custody law questoins please advise if you know?

My 16 yr. old sister wants to go and live with our dad. Her mother has legal custody and child support order. How old does a child need to be to decide who they want to live with? Also, what is the process for a change of custody? Is it a long drawn out process?Alabama custody law questoins please advise if you know?She needs to follow the judge's orders regarding her living situation until she is 18. If she wants to change custody, your dad needs to ask the judge for permission. This will require hiring a lawyer and it will probably take a month or two.