Extract the zipped package downloaded from customer account page to your desktop, in the extracted package you will find popcorn folder which is the wordpress theme.

You can install the theme in two different ways:

FTP: Extract popcorn.zip file and upload the extracted folder to /wp-content/themes/ folder on your server.

WordPress: Navigate to Apperance -> Add New Themes -> Upload page. Select popcorn.zip file. Press the Install Now button to upload and install the theme.