We have two options to manage the slider section including height.
1. If you select the Full Screen background, you can add the any image and the size will fit on the screen.
2. If you select the Responsive Image, you need to make your own image size and add it on the theme.
You can find the options to make the height small/large on the theme options Customizer. Please check all the available options for Slider section on Appearance > Customize > Featured Section Option.