One of the handiest plugins we’ve come across over the years is Regenerate Thumbnails. If you haven’t heard of this plugin yet (which is hard to believe with over 1 million installs), this plugin runs through your media library and refreshes your images based on your thumbnail settings in Settings > Media, as well as crop sizes defined by your current theme. This is really helpful for a number of instances.
If you’ve recently switched your WordPress theme, you might notice your images look a little funky. Maybe they aren’t the right dimensions, or maybe they just don’t match the images in the demo you previewed. This is because your site is likely showing images that were cropped to fit the previous theme, not the new one. The Regenerate Thumbnails plugin is a great place to start with this common issue. By running the plugin, it will go through your media library and create thumbnails based on the various crop sizes you have defined. This should kick your images into place and get something closer to what you expected.
You can download the plugin on the WordPress.org page, or you can add it to your site via Plugins > Add New. Once installed and activated, go to Tools > Regen Thumbnails and click the Regenerate All Thumbnails button to run the plugin. It will take a few minutes to run through your library and when it’s done, you can jump over to the front-end of your site and check out the results.