Answer:
United Palace Theater is really far uptown. It's on Broadway, between West 175th and West 176th Streets. The exact address is 4140 Broadway. You can call them at 212-568-6703.
To get there, take the S shuttle train (color code grey) east across 42nd Street, from Grand Central Station (East 42nd) to Times Square (West 42nd).
At the Times Square Station, transfer to the Uptown A train (of the A-C-E, the blue line). DO NOT take the C or the E. Only the A.
Take the Uptown A train to the West 175th Street Station. You will get out in Jay Hood Wright Park, near Fort Washington Avenue. Fort Washington Avenue is one block east of Broadway.
So, walk one block east on 175th Street, to Broadway. At Broadway, turn left, and walk north half a block to the theater.