When an images are uploaded to the media library, each image is saved at various sizes. These sizes are determined by the options on UXi General Settings > Media. Click here to learn more about media sizing on UXi General Settings.
If media settings have been updated on UXi General Settings, use the Regenerate Thumbnails tool to generate all images in the media library using the new sizes!
Note: This tool creates new thumbnails, but does not delete images saved using older media size settings. No page or post images will become invalid after updating sizes or re-generating thumbnails.