var slideWidth = 500;
it is in pixel you change it to 1024 pixel
var slideWidth = 1024;
or you can change slide & image width to 100% using CSS.
#slideshow #slideshowWindow
{
width:500px; --- width:100%;
height:257px;
margin:0;
padding:0;
position:relative;
overflow:hidden;
}
#slideshow #slideshowWindow .slide
{
margin:0;
padding:0;
width:500px; ---- width:100%;
height:257px;
float:left;
position:relative;
}