How to change homepage size?

Hi there,

http://www.eluniversodeingles.com

Is there a setting in the Geodirectory settings where I can change the size of the pages on my site? If you look at my homepage I would like the front banner picture to still be stretched across the page but appear to be smaller or zoomed out to that effect. Correct me if i’m wrong but is that the resolution? Giri kindly added a snippet for more about a month ago and i’ve tried changing the background-size setting from cover to different pixel sizes but not sure on how to change it really.

thanks in advance