How can a minor child in minnesota petition the court regarding his custody?

My 14 year old grandson is involved in a dispute with his father regarding the fact that he was in shared custody and would like to change it to full custody of his mother. Is it possible, probable for him to be able to do so.How can a minor child in minnesota petition the court regarding his custody?No. His mother could petition for full custody, and then the judge may agree to allow the son to choose. But alone, the son may not petition the court.