Image Sizes Available
- Featured Thumb Square 360×360
- Featured Thumb Rectangle 320×550
- Featured Image 720×400
You can download the plugin on wordpress.org/plugins/regenerate-thumbnails or simply search for Regenerate Thumbnails on Plugins → Add new in your WordPress backend to install the plugin.
After you have installed and activated the plugin, you can regenerate your thumbnails on Tools → Regen. Thumbnails.