Unzip the downloaded file, you should end up with a folder called "photoracer".
Upload the "photoracer" folder to your "plugin" directory (wp-content/plugins).
Make sure that the file permissions of the "photoraer" directory are such that the plugin is allowed
to write to it (otherwise, uploaded photos cannot be stored).
Go to the "Plugins" Wordpress admin panel and activate the Photoracer plugin.