Handy Plugin Lets You Regenerate All of Your Thumbnails for WordPress
Earlier today I saw tweet regarding the Regenerate Thumbnails plugin created by Viper007Bond. It allows you to quickly and easily regenerate the thumbnails for all of your image attachments. This is especially helpful if you’ve changed your WordPress theme and you need different-sized thumbnails or featured images.
The plugin lets you resize single images by hovering over their row in the Media Library. If you have WordPress 3.1+ you can also resize specific multiples images using the checkboxes and the “Bulk Actions” dropdown.
Regenerate Thumbnails is available for free from the WordPress repository.