@OP You mean harddisk space when you say memory right?
So, after a bit of investigation, I realized that DVD-RW disks can't just be reformatted and rewrited just deleting things, but that doesn't change the fact that it should've actually formatted when I wanted Windows to...
First off, using the term memory instead of disk space is confusing. Edit:
A DVD-RW? I didn't see that coming.
You might need to restart that from scratch to get back the written space on a multi-session disk, I've never used it as such so I'm just thinking out loud here.
I don't know how, I've tried everything from normally formatting it to manually deleting files. Maybe it really has just died...