Double Copy Each!

I recently acquired my first computer made by Apple, being that the newest version of the Mac Book Air. I already had a Apple ID, and have already bought some stuff. The first time I synced my iPad to my computer, it appeared on the iTunes Library all the items I've bought and have not downloaded to the Mac Air yet, and were on my Cloud, so I downloaded them and it was fine. Now, I bought some movies and music in my iPad after and the second time I'm syncing is giving me some problem: I have two copies of each item I've bought, one I have already downloaded to the computer and one that is set in the Cloud, an available download. What should I do to make the second copy disapear? I have already tried to delete each one of the extra copies, but it only hid my purchases from my Cloud!

Sorry for the bad English (: