Worth noting the difference between memory - which is what the computer uses to "think" and "process" current tasks, and storage often referred to as a hard disk, which is more akin to a book that you refer to. (Some vast generalisations in what I have said, but helping with a "picture" for a non-techie).

It's when storage/disk fills up that you might need to delete some files, but when memory runs low (as per the photo fromTedToToe you might close some programs or applications but a reboot is usually the best solution. No files would usually need to be shredded as an initial response to this error.