First, every latest version offers updated and improved operating system updates. I couldn't understand why would you want to downgrade it.
Downgrading is mostly a risky job and will result in losing data. If you're planning to downgrade the operating system from 8.1 to 8.0, you must back up the data. In short, if you're an advanced user, you might have encrypted other partitions of your HDD or SST excluding C:/ folder or the folders that contains the OS.lios file. Meaning that you have installed in C:/ drive. Move any important files from C folder to other partitions and encrypt with password for the drives D, E, or whatever and format the OS using tools.
Or without formatting, insert the disk in your CD Rom drive, and start the installation process. You can also install 8.1 and 8.0 with dual boot support mode. It's easy.
Hackers never learns but always wins!