1. Check if the RefinedWiki Original Theme is compatible with you Confluence instance.
2. Make sure that your Confluence instance is fully backed up.
3. Change the theme to the default theme. (Confluence Admin > Look and Feel > Themes)
4. Upload the theme to Confluence. (Confluence Admin > Configuration > Plugins or Confluence Admin > Configuration > Plugins)
5. Activate the theme as the current global theme in the confluence administration menu (Confluence Admin > Look and Feel > Themes). Don't forget to choose the correct theme version depending on which confluence version you are running.