Unwanted Files

Well, I'm going to try to download WoW and have some fun on my computer, but the only problem is I don't have enough disk space.
I have 9.88 GBs when I should have nearly 30GBs. The whole game is 20GBs but I have no idea how I can free that much.

I deleted all my games, I ran CCleaner, I formatted but nothing seems to work.
After running CCleaner I barely cleared anything, maybe even nothing at all.
I ran Disk Cleanup but that only gave me a few MBs.

Does anyone know of any files that I don't need that I can delete on my computer?

I go into My Computer and go to my C Drive and there's a bunch of files such as "076f047f55da145261d30a02913d8186" but I don't know if I should clear those files or not, they seem like they're important, but I don't know for sure.

TL;DR How do I regain all the space on my computer?

All the space: format.

Though you could uninstall the games you don't have, delete the savegames etc...

Formatting never worked for me. My total space is 38GBs, I should have 32GBs, the other 5GBs are stuff for my computer, idk.
I've deleted lots of files so far, useless ones and I'm bumped up to 14.7GBs, only 300MBs left.

Now my real question is:
Are the files that are named "076f047f55da145261d30a02913d8186" etcetc. useless? They're taking up quite a bit of space but I have a feeling that if I delete them it could mess up my computer.