the reggedit files and the program files.. And I can't reinstall expect on a seperate drive, because the computer says "not enough space".
I don't use Windows myself these days. I'm totally macOS and Linux since 2006.

But I know with RegEdit(editing the Registry),
if you get that wrong, you could end up with a system that doesn't boot and having to reinstall Windows. So be careful!.
Check the Control Panel > Installed programs, and see if Bluestacks is registered as being installed there, and that might allow you to clear it. You'll find the Bluestacks EXE program itself under /Program Files/Bluestacks, along with the associated files. Try deleting that or moving it to temporary storage off the PC like to a USB hard-drive or USB thumb-drive, and that might give you enough free space to reinstall Bluestacks the normal way.
Bluestacks on a Mac requires about 8GB, I presume it's similar for Windows.