Changing the slideshow on a theme

I downloaded a free theme that has a built-in slideshow viewer and I am trying to change it using a plugin. I have used this plugin on another theme and it works fine, but for some reason the site I want it on doesn't change when the plugin is installed and activated. The theme is called Musica and the built-in slideshow can be seen here . The slideshow I am trying to use is JSJ Gallery Slideshow. Any help would be appreciated. Thank you.