This article is from the FAQ, by with numerous contributions by others.
There are two ways:
1. You can file for a status change with INS by sending in your
application through mail. You will have to check with your ISO or INS
about the forms and fees, etc. But this process of late has been
taking a few months. If you have to join school by then, consider
2. Fly over to Juarez or some such place outside US and apply for F1. We
did that in the case of my wife successfully a few days back. They
will need I20, proof of financial support, etc. - the normal stuff
required for F1. It was not a problem at all.