When you import our demo content it can take several minutes depending on the speed of your server. Each time the button is clicked it will import the content, so if it is clicked twice it will import everything two times. There are some ways to get rid of duplicate content.
Method 1: WP Reset Plugin – This plugin is the fastest way to get rid of content. However, it will remove all content from your database and leave the default theme activated. It does not remove plugins, but will deactivate them and remove all pages, posts, menus, sliders, widget data, theme options, etc. Basically it removes all the content that you imported from our theme. Only do this if you are able to start over. Click Here To Download.
Method 2: Manual Removal – This method will take longer and simply involves manual removing of duplicate items. For example, go to the appearance > menus and delete duplicated items one by one. Do the same for pages, post, sliders, etc.
Method 3: Deleting the Database -- If Method 1 doesn't work for you then deleting the database will help you out. If you've never done it, you'd better ask your hosting company to do it for you.
Re-Import of the demo content:
You can use any of the 3 methods above to remove the existing content and then import again the Demo Content.