Step 1: take the uptown (northbound) _R_ or _W_ train (Yellow Line on the subway map) from Whitehall Street-South Ferry to Lexington Avenue-59th Street.
Step 2: at Lexington Avenue-59th Street, transfer downstairs to the #4 or 5 subway lines (Green Line). Take the uptown (northbound) #4 or 5 train from 59th Street to 86th Street.
Step 3: at 86th Street, transfer upstairs, at street level, to the M86 bus. Take the westbound bus, going to the West Side, from Lexington Avenue and 86th Street to 84th Street and 5th Avenue.
I hope this information is very helpful.
Good luck
Native New Yorker
Alternatively, you can get an uptown R or W at Whitehall Street, and transfer to an uptown 4 or 5 at 14th Street/Union Square, then get off at 86th as described above.