Problem with the size of image in the slider

Hi! I don't know why when I upload the image in the main slider, the photos look so small. The size of both image are 1920x1280 and 1214x1473, should be big enough to fill the space... I tried to follow the instructions of the theme, but in “Customize => Theme Options => Featured Slider” I don't have any option apart from upload the images and page and the number of slides. I hope someone can help me, Thank you! http://laiasaga.byethost6.com