The slideshow's height is determined by the height of the largest slide image. Uploading images with identical dimensions for your slideshow banners is the best way to ensure consistency (see our Image Size Guide here). If images have different dimensions, this often results in large amounts of whitespace underneath the smaller images to fill the container and avoid cropping.
Use the Adaptive Height Setting
The Adaptive height slideshow setting automatically adjusts the slideshow container based on the height of the individual images in each slide (no more whitespace below).
Open the theme editor (Customize), then the Slideshow section to Enable adaptive height.