Hi i did change my status from B1 to F1 but in interview i had tole them that i am to give exam to pusue my college, so u have to declare prospective student. thats what they wrote in my annotion of visa , to give exam and for higher stjudy. I changed in 28 days. One fren of my did the change too from b1 to H1 but he was acceptd by John hopkins university and the university did everything for him., u may try it too.

Good luck.