How to move an entire div element up x pixels?

$('#div_id').css({marginTop: '-=15px'});

This will alter the css for the element with the id "div_id"

To get the effect you want I recommend adding the code above to a callback function in your animation (that way the div will be moved up after the animation is complete):

$('#div_id').animate({...}, function () {
    $('#div_id').css({marginTop: '-=15px'});
});

And of course you could animate the change in margin like so:

$('#div_id').animate({marginTop: '-=15px'});

Here are the docs for .css() in jQuery: http://api.jquery.com/css/

And here are the docs for .animate() in jQuery: http://api.jquery.com/animate/

$('div').css({
    position: 'relative',
    top: '-15px'
});

In css add this to the element:

margin-top: -15px; /*for exact positioning */
margin-top: -5%; /* for relative positioning */

you can use either one to position accordingly.