Here you can find answers due to page speed testing:

Gzip compression:

You have to enable it on server side: http://gtmetrix.com/enable-gzip-compression.html

Leverage browser caching:

You have to also configure it on server side: http://gtmetrix.com/leverage-browser-caching.html

Specify a Vary: Accept-Encoding header:

This should be configured also on server side: http://softstribe.com/wordpress/vary-accept-encoding-header-in-wordpress

Enable Keep-Alive:

This should be configured also on server side: http://softstribe.com/wordpress/how-to-enable-http-keep-alive-in-wordpress/

Minify JavaScript:

Solution for this is some cache plugin (we can recommend WP super cache).

Serve scaled images:

This problem is based on responsivity. GoodStore theme has to serve images that are nice on every devices.

Minify CSS:

Solution for this is some cache plugin (we can recommend WP super cache).

Optimize images:

Please try this plugin: https://wordpress.org/plugins/ewww-image-optimizer/