I m sure you can change your status from B2 to F1. For changing your status i belive you dont have to leave USA. You can just download form from www.uscis.gov. You can do your self but you have to becareful in this. Becuase you are here with B2 and if you able to show finacial source than you can, plus explaination letter too. But, if you go through immigration lawyer than it rally helpful and there is lots of nepali lawyer in NY city. i hope this help you little bit... if there is anything i can do let me know.

Thanks