Don't Delete Anything
If you have a device that features 8GB or 16GB of space, you might be worried about the amount of space the iOS 9.0.1 requires to install. The answer is: Not much.
We installed the iOS 9.0.1 update on the iPhone 6 and iPhone 5 Over-the-Air and we weren't required to delete any files to make room for the update. The iOS 9.0.1 update is, again, about 20MB in size so you shouldn't need much to install.
Those of you with virtually no storage space available should be able to install this update without any probems so don't go deleting files and apps before you try.
If you're unable to install the update, you can plug your iPhone or iPad into iTunes and install that way. Keep that in mind for future iOS updates.