In the theme editor (Customize) => Section, click Slideshow
If you want to change the style slideshow => Style Slideshow
You can change the width and height Slideshow, some options below:
In the Slideshow section, click Add Image slide.
You can settings
Image 1, Image 2, Image for mobile, Position Image, Position Text content, Background Slideshow, Overlay Image
You can Settings
Top Title, Heading, Sub Heading, Button1, Button 2
If the text is blank Text or Button will disable