In order to install a Zen Cart template, you need to upload the installation template package in the includes/templates folder inside your Zen Cart installation  directory.

Then you need to extract it. The easiest way to complete this is to use cPanel > File Manager.

Once the template is uploaded and extracted, you should log in to the Zen Cart admin area.

Once there, go to the Tools >Template Selection section. Click on the Edit button and select the new template from the drop-down menu. Click the Update button.

Visit your Zen Cart main page, refresh it and check the result.