function ChangeVisibleImage( ElementNr ) {

  var div_box = document.getElementById( 'product_item_mainpic' );
  var div_box_oldpic = document.getElementById( 'product_item_' + ElementNr.toString() );
  var div_box_newpic = document.getElementById( 'product_item_' + ElementNr.toString() );

  for (var nlauf = div_box.childNodes.length -1; nlauf >= 0; nlauf--) {
    div_box.removeChild( div_box.childNodes[ nlauf ] );
  }

  for (var nlauf = div_box_newpic.childNodes.length -1; nlauf >= 0; nlauf--) {
    div_box.appendChild( div_box_newpic.childNodes[ nlauf ].cloneNode(true) );
  }

}