If you buy music, movies, and TV shows with iTunes on your iPhone, iPad, iPod touch, or computer, you can easily re-download content on other devices on demand thanks to iTunes in the Cloud. That means you can buy a movie on your iPhone and later download it on your computer through iTunes whenever you'd like. Even better, if you need to delete iTunes content to save space on your Mac or PC, you can re-download iTunes purchases at a later time.
How to re-download music, movies, and TV shows to your Mac or PC
Launch iTunes on your Mac or PC.
Click iTunes in the top menu and then Preferences.
Click on Store along the top navigation in the window that pops up.
Make sure the option for Show iTunes in the Cloud Purchases is checked and click OK.
Click on either the Movie, Music, or TV shows icon in the top left navigation.
Click on the first tab labeled either My Movies, My Music, or My TV Shows depending on the content you picked in step 5.
Click on the cloud icon next to the movie, music track, or TV show you'd like to download.
That's it. You can see the progress of your download by clicking on the downloads icon in the upper right hand corner.