Yes, there is an elevator in the parking garage. It's not the main part of the parking garage, though. If you go all the way to the top, there's a ramp that takes you over to some additional parking in the Ainahou tower. I don't believe the door to the elevator is marked, but it's there.

As for which tower to request, most people say Ainahou, but I'm not sure it really matters. (Nor do I think "ocean view" is worth anything extra, as you're a block from the ocean and there are other hotels between there and the ocean.) Just consider it a room (relatively spacious -- 300 to 350 sqft -- by Waikiki standards) to sleep in with some extra amenities (mini-fridge and turndown service) in a good location, and your expectations will be about right.