The plugin adds three cropped thumbnail sizes for use upon activation.  These are produced when images are uploaded to the media library.  Their sizes are: 540x388px, 540x192px, and 270x192px.  If your slider is not aligned as in the example, you may need to re-upload the featured images for the posts displayed. Or, use a thumbnail resizing plugin to do this all at once.  Of course, the latter option should be chosen only if the image library is small.