If the Related Products images in your Twenty Thirteen WooCommerce store are blurry there is an easy fix. Go to WooCommerce > Settings > Products and change the size of the “Catalog Images” from 150 x 150 to 300 x 300. Now you HAVE to regenerate the thumbnail images in order to render your changes. So you need to install a plugin called Regenerate Thumbnails by Viper007Bond. After you activate this plugin you will find it under Tools in the Admin panel of WordPress. Go in there and click Regenerate All Thumbnails. Done!