Hello Milena,
Please add the below CSS codes in Appearance > Customize > Layout/Design Options > Custom CSS to reduce the height of the slider on Home Main Content Area.
.slider-section.widget-slider img {
height: 300px !important;
}If you want to increase/decrease the height, you can increase/decrease the pixel written above.
Let us know about the results.
Please use the respected theme forum for the theme specific queries.
Regards
Acme Supports