1. In your Metro Start Menu, move your mouse to the lower left corner and the Start menu pops up. Click on Search.
2. Type regedit in the Search Apps text box. Click on the regedit.
3. Click on Yes in the User Account Control box.
4. Now the Registry Editor opens. Click on the file menu and click on the Export.
5. Now save the registry backup to your system. That are the complete steps to backup Windows 8 registry.