Resize main photo in frontpage photo gallery 1

[domino3]

Can someone tell me how to set the size of the enlarged photo in a photo gallery, if it is possible. I have the photogallery set to slide show and the thumbnail photos are fine, but the main display photo is huge. I've tried making the file itself smaller, but that ruins the resolution and leaves the width and height of the photo the same. Alternatively, is it possible to change the width of the montage display from the default, and if so how?

Thank you.