(Reuters File Photo)
Why does it work?
The reason to get increase space is because it is trying to make room for the movie and meanwhile iPhone also cleans installed apps to remove data, cookies and histories which no longer be needed.
One Reddit user was surprised with the amount of storage space and commented "That's actually clever. I just went from 800 MB to 4.9 GB free space."
The article also suggested that renting the same movie many times could free up even more space.
There is another trick to increase storage, when 'cannot download' prompt is shown on your phone, do not touch it for a while.
A clean up process seems to run in the background until you hit 'OK or Settings' button.