Change the height of the header image?

Hello, I'm using Free High Responsive theme. Is it possible to change the size of the image of the Header Media image. Now on a classical screen size (1920 x 1080 pixels), the height of the image is very small, around 430 pixels for a lenght of aournd 1900 pixels. Does it exist way to change the ratio, enlarging the height of the image? The coping option when we select the images and no effect here. Have you got an idea? Thanks you in advance Regards