Size of Content Boxe images on Homepage

Hi there

First off, thank you for a superb theme. Hard to believe that it is free. Beats most premium themes I have used.

I want to show images instead of icons in the Content Box area on the homepage. I want them to sit on top of the text (and so have changed the alignment to “top” instead of “left”). So far, so good.

But I also want these images to spread across the full width of each column (460px). When I upload them in the Theme Options area, they are automatically changed to 250×83 px – not nearly big enough! Can you give me a clue as to where I change that setting? My original images are 450×150.

See the home page here: greenworx.ie

Many thanks,
Derry