They're VERY stuck together. They used a pretty good packing tape... I'd say a hair dryer would work as it's generally not hot enough to harm anything unless you have it up against the cardboard itself. I wouldn't use a heatgun obviously, but a hair dryer MIGHT work. I'm not freaked on the packaging since I don't care, but if you wanna save it, more power to you.
iFett's idea of goo gone might work too, especially if you can just get under it enough to spray some in and gently and meticulously work the tape backwards. It, in general, won't harm cardboard. You might have to let it dry, but it usually doesn't hurt cardboard.
I was looking my shuttle over... It's a neat ship, but not for what it ultimately was intended to be. It's cooler as a small fighter than a shuttle... The cockpit is pretty cramped and the ship's size is kind of unrealistic IMO, but as a little Mando fighter I think it has some hope so I'm going with that I think. I like that the wings fold up so you can see the engines. The Hasbro guys seem to like looking at fictional engines these days, between this, the Snowspeeder, the Cloud Car, and the Speederbike.