Changing size of header image on front page

Hi. I have my site on Snowfall theme, which I like v. much. Trouble is, I’ve noticed when the site displays on a mobile phone, the header image on the static front page is taking up a huge amount of space, meaning that the text on the front page isn’t visible unless you scroll down the screen a long way, which makes it user unfriendly. I’d like to change the size of this header image space or delete the space altoghether…there’s an optionto delete the image but it still leaves the space filled with background colour. I’m not sure where to look in the code for this or how to change it. I don’t want to change the size of the images on the other pages as it doesn’t seem to be doing this on them, only on the front page. Advice on where to find the offending code and what to change it to would be much appreciated. Many thanks