I recommend that you move the folder plugin-data to your wp-content folder. Remember to change the css location option in the settings page for this plugin. Or edit directly: wp-content/plugins/superslider-menu/plugin-data/superslider/ssMenu/custom.css. Alternatively, you can copy those rules into your WordPress themes, style file. Then remember to change the css location option in the settings page for this plugin.
Check this url in your browser: http://yourblogaddress/wp-content/plugins/superslider-menu/plugin-data/superslider/ssMenu/custom.css If you don't see a plaintext file with css style rules, there may be something wrong with your .htaccess file (mod_rewrite). If you don't know how to fix this, you can copy the style rules there into your themes style file.
You can upload your own images to http://yourblogaddress/wp-content/plugins/superslider-menu/plugin-data/superslider/ssMenu/custom
Make sure you specify category names, or ids.