Updating the Easy Plugin Demo core plugin is straight forwards. WordPress will prompt you that an update is available in the same way as all plugins hosted on WordPress.org.
As a result, you may not see that updates to the Premium Pack are available if you are only accessing the network admin portion of your site. i.e. the URL ending /wp-admin/network/ (https://<domain.com/wp-admin/network/).
To ensure you receive updates regularly, you should log in to admin for your primary site (normally the site with ID 1). i.e. the URL ending /wp-admin/ (https://<domain.com/wp-admin/).
In order to update plugins, you must have the WordPress Super Admin role.