Extract zip in the /wp-content/plugins/ directory.
Activate the plugin through the 'Plugins' menu in WordPress.
Open the plugin management page, which is located under Tools -> Generate Thumbnails. If you get plugin warning, that means either your theme does not support WordPress Post Thumbnails feature or your WordPress version is lower than 2.9. See related links for more information.
Set overwrite parameter, if you want existing post thumbnails to be overwritten by generated thumbnails.
Set the number of the post image, that you want to be used as your post thumbnail.
Click on Generate Thumbnails and wait until process is finished.
Requires: 2.9 or higher Compatible up to: 3.1.4 Last Updated: 2010-7-15 Downloads: 26,840