Changing the aspect ratio of the carousel changes the height of the carousel.
Select the carousel by clicking on the module once, then use the Aspect Ratio menu on the toolbar to select a new ratio.
For the absolutely shortest height, use 4 x 1. However, this aspect ratio is bit too extreme for most uses. Try 3 x 1 instead for a more pleasing ratio.
Once the ratio has been changed, it may be necessary to reposition the images. To do so, click on the image to select it (not the thumbnail), then click the Crop icon. You may now click and hold on the image to reposition as desired.
Widescreen or landscape photos will look best in the carousel. See our recommendations for image sizes.