You will need to take the subway to reach Manhattan. Take a "Howard Beach" AirTrain from your terminal to the last stop. At Howard Beach station, take a Manhattan-bound "A" train to "Fulton Street"; Wall Street is a short walk from there.
There is also a slightly less expensive option: From JFK Terminal 4, you can take a Q-10 or Q-10 Limited bus to Lefferts Boulevard and Liberty Avenue, and board the "A" train to Manhattan from there. This route will likely take a little longer than the AirTrain/subway combination.
You will need to take the