My website still not secure regardless of a certificate

Hi
I bought a certificate for secure website, it is installed by Tsohost and I have change the pictures to https and still it is says it is not secured.
I have been told that it could be the theme radience
xxxxx this is the theme editor

Do I need to do something to it? and where?
xxxxx
Theme Name: Radiate
Theme URI: https://themegrill.com/themes/radiate/
Author: ThemeGrill
Author URI: https://themegrill.com/
Description: Radiate is a clean, creative and light retina ready responsive blogging theme supporting parallax header image. It integrates primary color option, custom background, custom css and few other features through WordPress customizer. The theme is translation ready and you can get free support on https://themegrill.com/support-forum. View demo at https://demo.themegrill.com/radiate. Available Translations -> French.
Version: 1.0.3
License: GNU General Public License v2 or later
License URI: https://www.gnu.org/licenses/gpl-2.0.html
Text Domain: radiate
Domain Path: /languages/
Tags: light, white, two-columns, right-sidebar, responsive-layout, custom-header, custom-background, custom-menu, custom-colors, post-formats, sticky-post, threaded-comments, translation-ready

Resetting and rebuilding styles have been helped along thanks to the fine work of
Eric Meyer https://meyerweb.com/eric/tools/css/reset/index.html
along with Nicolas Gallagher and Jonathan Neal https://necolas.github.com/normalize.css/
and Blueprint https://www.blueprintcss.org/
*/

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