How to Rebuild Thumbnails in WordPress

1. Log into your WordPress website.
2. Click 'Media' from the menu on the left, then click 'Library' from the sub-menu.

3. Click the 'Edit' link under the name of the image you wish to edit.
4. Click the 'Edit Image' button. This will open the built-in WordPress image editing tools, such as resize, rotate and flip. You will also see the image's current thumbnail image on the right.
5. Make your changes to the image using the tools.
6. Place a mark next to 'Thumbnail,' then click 'Update Media' to rebuild the thumbnail on your WordPress website.
7. Repeat this process for each thumbnail image you would like to change.