Cannot revert to Windows 8 after installing Hyper-V Server 2012 R2

I own a laptop with a pre-installed Windows 8. I've installed Hyper-V Server 2012 R2 on top of it by mistake, and now I would like to get rid of it and revert it back to Windows 8. I've tried doing so by a backup USB, though it doesn't seem to work. Is there anyway to do this without having to use a disc? I haven't received one when I bought it.

Thanks for any help in advance.