I have been accepted to study through an online university and want to change my visa

My wife and I both have working Z types for teachers, I will start to study full time very soon and would like to change my Z type to a spousal type as i will not work. We are both South African. The reason why i want to change it is so that i can get rid of my agent contract. We both currently live in China.
Please advise is this possible, and how.
Thank you.