You nee to Download Regenerate Thumbnails WP Plugin. Why I recommended this plugin? Because this plugin is the perfect way to recompile you entire WordPress Thumbnail. Using Regenerate Thumbnail Plugin. You can batch command and re build you thumbnail.
The Developer has said, why this plugin really awesome useful
This is very handy if you’ve changed any of your thumbnail dimensions (via Settings -> Media) after previously uploading images or have changed to a theme with different featured post image dimensions.
This plugin will handle it automatically. Change Thumbnail size not a big deal anymore. Read the rest of this entry »