You deleted everything from your USB key or a drive, so there should be enough free space to copy the new files, but you still get the not enough free space message in Mac OS X? This is what you need to do.
Some web pages have the Save image As... option disabled on a right click when you try to save an image. Let me show you how to get that image anyway using Firefox.
The latest photo of Saturn you are about to witness is so perfect and mind-blowing you will most probably have hard time believing that it is not fake.