I am not a computer genius, but,
Memory and drive space are not the same thing. Memory is exactly that memory, and drive space is storage. I would probably try to clean up the drive and get rid of unwanted junk, or better yet go to www.newegg.com and buy a new harddrive with a lot more space (terabyte, 800gb, 500gb, etc). If you still have the disk of your current operating system, you can just instal that on the new drive (unless we're talking windows 95). Pretty easy to do even for someone with no computer skills. Google "how to instal new hard drive" and you should be in business.
That's what I would do.