Clean your Media Library from the media which aren't used in any of your posts, gallery and so on. First, before using this plugin, make sure you have a proper backup of all your files and database. This is the most important step on the usage of this plugin, you can't trust any file deletion tools. The Pro version of this plugin brings also scanning to the /uploads folder and will detect which files aren't registered in the Media Library and not used in your content. Retina images are also detected and supported, shortcodes, HTML in sidebars and of course your posts, pages and all post types.
UNIQUE PLUGIN. Such a plugin is difficult to create and to maintain. If you understand WordPress, you probably know why. This plugin tries its best to help you. Get used to it and you will get awesome results. This is the only plugin to propose those functions and even a dashboard to cleanup your WordPress install from unused files.
This is pro version of this free plugin Media Cleaner — WordPress Plugins