To get to the Polynesian resort from the Art of Animation resort you will want to board a bus that will take you to the Magic Kingdom. From there, board a bus to the Polynesian, or take the monorail there. Ohana is located within Disney’s Polynesian resort, which is on the monorail resort route. To get back to the Magic Kingdom, take the monorail from the Polynesian, or if you feel like trying some different transportation, take a short walk to the Ticket and Transportation Center from the Polynesian and board the ferry boat to the Magic Kingdom. At the end of your time in the Magic Kingdom, you can board a bus back to your hotel.
Or, take a cab. That is clearly the easiest.