I am assuming you are in NY. The original lease has expired, so now you are on a "month to month" lease. You have to give him 30 days notice in writing. You can write this document up yourself---your name, his name, date, address and the words, "30 Day Notice." If he moves, good, otherwise, you may have to take him to housing court.
Double check the procedure above with a housing advocate, but that's what I had to do.