Please go to your theme options list and click of the very last option (screenshot). After clicking on the demo you would like to import, then go and click Import button (screenshot).
Let us know if you need further help.
The only way to remove the “double pages” is to delete them manually. Each page uses Page Builder to populate it with elements. You have to install and activate required plugins (see the message in your dashboard), in the list there is Visual Composer plugin as well.
After installing plugins you will be able to see the Visual Composer elements and use them in every page.
Let us know if you have further questions.
