You can change from Tourist visa to Student visa after entering. However, you should be very very careful because: (1) You must not try to change visa status within 60 days (90 days to be safe) of entering US. That will trigger a case for Visa Fraud, because it shows that you didn't reveal your intention when you applied for tourist visa. (2) You would be safe if you asked the officer at the port of entry to stamp as a prospective student (I don't know whether you have to do it when you apply at consular office). If the PoE office stamps your papers with Prospective student, then you can find good college, get admission and change from tourist to student status without problem. (3) If you don't have Prospectivs student stamp, the safest thing is to go back home, reapply for F1 and come back. I guess that the chances of denial are very less in this way.