jQuery(document).ready(function() {
  window.setTimeout("change_logo()", 3000);
});

var $logo_index = 0;
function change_logo() {
  jQuery('#logoimg').attr('src','http://yourposition.ch/wp-content/themes/yourposition/gfx/logo/'+$logo_index+'.png');
  $logo_index++;
  if ($logo_index == 6)
    $logo_index = 0;
  window.setTimeout("change_logo()", 3000);
}