How to make images in gallery element bigger than the deafult?

Hello, we would need to make the images in the gallery element bigger than the default you get. In a previous thread started by us about the hovering options in the gallery element, part of the code you provided, allowed the image size to be made bigger. We just cant't extract the specific part of the code commanding only the size of the image. Would you please provide this for us? And feel free to access the site we are developing on a temporary url, the support access is granted. Thank you so much!