my son now passed 9th std frm cbsc board now i want to change him to kerala state board what is the procedure?

It will be difficult to change your son from cbse to state board when he is in 10th standard. But you can try if any state board college is ready to give admission to him then you can try. There will be a long process because changing a candidate from central board to state board during 10th use to be tough. Registration for 10th always happens in 9th. So try to finish your 10th and change thats a normal practice. Procedure will be explained by the board, but you must get admission in any state board and even cbse should allow you to take admission then only you can change.