Changing header image size on front page

Hi. I have my site on Snowfall theme, which I like v. much. When the site displays on a mobile phone, the header image on the static front page is taking up a large amount of space, meaning that the text on the front page isn’t visible unless you scroll down the screen a long way, rendering it user unfriendly. I’d like to change the size of this header image space or delete the space altoghether. I’m not sure where to look in the code for this or how to change it. I want to change the size of the header image only on the front page. Advice on where to find the offending code and what to change it to would be great. Many thanks