If you already have a Joomla based website and want to change its design, you need to use the template installation method.
This method lets you to install a Joomla template and all the necessary extensions.
Once you have your Joomla template downloaded on your computer, login to the administrative area of your Joomla website and upload the template through the Extension Manager (Extensions -> Extension Manager). The process is the same for templates, modules, plugins and components.
In “Upload Package File” tab, press the “Choose File” button and choose “###_template.zip” file from the “joomla” folder of your template package. You’ll see the installation confirmation massage.
To install the Joomla template, press the Upload & Install button.
When installation process is complete, please activate the template. In the top menu, navigate to “Extensions > Templates” tab.
On this page, you will see a list of the installed templates available for your site and the administrative area. Locate the one you want to use on your site and click on the star icon on it or select the new template and press the “Default” button. Now you can check the new appearance of your website: