From Ueno, I'd go to Nippori station via JR Joban express line, JR Yamanote, or JR keihin-tohoku line. All three lines are about 5 minute ride. From there take a taxi to yoshiwara--about 1,500 yen ride. If you don't know how to say it, just say "soapland" and you'll get there.
Hope this helps!