how to enqueue javascript

Hi guys,
My theme uses old version of Jquery and it causes conflicts with many plugins. (https://wpdance.com/wordpress-themes/risusunit.html)
I need help enqueueing the javascript in header.php here.

<script type="text/javascript">
		jQuery('ul.sub-menu').each(function(){
			jQuery(this).before('<div class="div-sub-menu"></div>');
			jQuery(this).appendTo(jQuery(this).prev());

		});

		jQuery('.menu li').each(function(){
			if(jQuery(this).children('.sub-menu').length > 0) jQuery(this).addClass('parent');
		});
		jQuery('.menu-top .menu > li:first').addClass('first');
		jQuery('.menu-top .menu > li:last').addClass('last');
		jQuery('.nav .menu > li:first').addClass('first');
		jQuery('.nav .menu > li:last').addClass('last');
		jQuery('.sub-menu').each(function(){
			jQuery(this).children('li:first').addClass('first');
			jQuery(this).children('li:last').addClass('last');
		});

	</script>

Does anybody know how to fix this?