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Any purchased Music, Movies, or TV shows from iTunes are always available for redownload if you delete them from your iTunes Library. The following article will show you how to locate the Purchased section on iTunes or your iOS devices. There is not a step you need to take, once you make the purchase they are associated with that Apple ID.
I hope this helps,
Joe is right, but a few caveats: Don't delete your movies and TV-Shows without keeping a backup. YOu cannot rely an the App Store to keep the items forever for downloading again.
Previously purchased items might not be available if they're no longer on the iTunes Store. If you changed your Apple ID from one country to another, you can’t download items you purchased in a previous country.
And you need to be in country, where iTunes in the cloud is available. Check this list: