After installing the theme, you should see a Notification Bar where you are asked to install and activate the plugins coming with the theme. You need to install and activate the required plugins.
Please note, you should find a Notification saying ‘Please verify your purchase code‘ in this section. The Ronby Extensions plugin download link will be given to you only after you verify your purchase code by clicking on the link given in that notification. After downloading the plugin, visit the Plugins > Add New page and install and activate the plugin you just downloaded.