Go to Appearance > Customize >Alnilam theme options > front page slider two
Alnilam-Pro theme content of an extremely powerful and flexible carousel/slider. you can add three images and three carousel captions for them.
In this section, you can customize,
Slider header
Carousel caption one
First image of the slider
Carousel caption two
Second image of the slider
Carousel caption three
Third image of the slider