If you've got less than 6GB of free space, you're going to run into plenty of other problems as well. You need to free some space or upgrade the drive. Right now, your computer doesn't have enough space to use for virtual memory the way it's designed, most likely, so you're getting heavier than normal disk activity and slower operation than you should, possibly to a very significant degree. This is something you should definitely take care of, and not just by circumventing the issue long enough to install this update.
jW