The Polygon Documentation (free version)
Installing The Polygon (free version)
To install this theme you must possess a functioning version of WordPress already installed. For information about installing WordPress, please see the WordPress Codex - https://codex.wordpress.org/Installing_WordPress
Upload via FTP:
First, unzip the zip archive you have downloaded. Search the folder named The Polygon-Free.zip. Open this archive and upload The Polygon folder to your server via FTP into the directory /themes/ of your WordPress installation (wp-content > themes).
Upload via WordPress admin:
Installing WordPress https://codex.wordpress.org/Installing_WordPress
Go to your WordPress admin, and go to Appearance > Themes > Add New: then upload the file "the-polygon-free.zip".