Use the theme option on Catch Responsive to make the website your own. You are free to use the images in the slider, though you will probably want to use your own. The dimensions of those images are 1200×514. They need to bee the Featured Image of a page. You choose which image/page pairs will show in the slide show under Appearance > Customize > Featured Slider.

For more information on the Catch Responsive theme see the instructions and check the support forum.