Just a quick tip. Since what amazon had for free was only the full version key.. you can download that from the app store and then grab version 3.0 directly from the android market so you will get the updates to the core program at a normal pace
I grabbed both downloads on the Amazon market. My bet is ONLY Amazon's app store will let you update. If you are worried about it I would just re-download the install. Otherwise your Amazon app store should just let you update through there!