Thank you so much for using our theme. If you need to make the slider post random, you need to customize the theme because such options is not available on the theme. If you are familiar with codes you can find the codes and try to take help from codex. Find the theme codes for slider inside acmethemes/hooks/slider-selection.php file and in the query you can use random-post parameters. Please try with the help of Google. It will help to learn codes as well.
Let us know if you faced any confusion.