If you have a site with us, you have one site with a dedicated theme, but if want to change the plugin, follow this tutorial.
go to Appearance » Themes from the left sidebar of the WordPress admin panel.
Change WordPress theme on live website
On this page, you need to hover the mouse cursor over the theme you want to use and then click on the Activate button to change the WordPress theme.
Now you can visit the homepage of your website to see the new theme in action.