Themes has been duplicated

I’m not sure why all themes appear to be duplicating themselves, have you tried disabling all of your plugins to ensure there isn’t a confliction occuring?

You can also use an FTP client to manage your themes. Connect to your web space using the FTP client and locate the wp-content/themes folder, each theme you have installed should have its own sub-folder within. You can delete themes by deleting the respective folder.

You can also try enabling the default TwentySixteen theme too to see if their is an issue with the theme you’re using.

Hope this helps.