The only memory on your hard drive is the cache built into it.
Hard drives have Storage Space. I don't mean to nitpick but folks giving out help should be correct with terminology.
Storage and memory are similar but not interchangeable.
How would any program know what you consider to be useless files? To carry that question further I would state that there are no useless files. Only files you don't think you need at the moment.
I suggest you form some sort of system to organize your files so they can be easily accessed. Take my word for it, sooner or later you will have a need for most stuff on your drive. If you want to archive files that you consider clutter then burn them to CDR or DVDR. You can fit a lot of stuff on one disk.