Articles from a specific category in the Front Page

Hello. I have a wordpress theme with a custom Front Page already created by the theme with a little Slider and then articles.
Because is only a simple custom front page without options in the Theme Menu, i can’t select what posts are shown in the Slider.
I just want to show articles from a specific category in that Slider, because now are the latest articles.
I tried to find a workaround with the following code but didn’t succeed:

<?php
query_posts('cat=4');
?>

and also with that:

<?php
query_posts('category_name=CategoryName');
?>

But no success.
The custom home page code is: https://pastebin.com/MMZFNKVy
The website where you can see an example of the theme is : https://leadrights.com