Delete/reinstall discover

I am using discover theme on WP 3.6.

Subsequent to editing the theme, I realised I should be using a child theme.

I created a child theme and then updated discover, which failed.

I then tried to delete the folders manually so I could reinstall the theme, but certain files would not delete.

I then copied the original theme files back into the folder. This made the theme available again in the admin section to use, but activating or previewing failed.

Then I ran out of ideas and came here for help. How do I delete this theme properly so I can reinstall it. It’s something to do with certain files being installed but not having the permissions to remove them. I’m stumped