How can I change header to random rotate

<?php if (strpos($bfa_ata['configure_header'],'%image')!==FALSE AND 
$bfa_ata['header_image_javascript'] != "0" ) { ?>

var HeaderImages = new Array(<?php echo implode(",", bfa_rotating_header_images()); ?>);
var t; var j = 0
var p = HeaderImages.length
<?php if ($bfa_ata['header_image_javascript_preload'] == "Yes") { ?>
var PreLoadImages = new Array()
for (i = 0; i < p; i++){
	PreLoadImages[i] = new Image()
	PreLoadImages[i].src = HeaderImages[i]
}
<?php } ?>
function RotateHeaderImages(){
	if (document.body){
		HeaderImageContainer = document.getElementById('imagecontainer');
		HeaderImageContainer.style.background = 'url(' + HeaderImages[j] + ') <?php echo $bfa_ata['headerimage_alignment']; ?> no-repeat';
		j = j + 1
		if (j > (p-1)) j=0
		t = setTimeout('RotateHeaderImages()', <?php echo $bfa_ata['header_image_javascript']; ?>000)
	}
}
window.onload = RotateHeaderImages;

<?php } ?>