Rent a flick
But don't actually. Simply go to the iTunes store and double tap Rent on a movie with a large file size, around 6 GB (we recommend LOTR!). Do not fear, your account won't actually be charged, assuming you have under the available storage room necessary for download. After you receive the automated pop-up stating you're out of storage, check your settings! You'll be amazed to see multiple megabytes (and with any luck, gigabytes) free. Repeat as desired.