<a href="#" class="büyüt">BÜYÜT</a>
<a href="#" class="kücült">KÜÇÜLT</a>
<div></div>

div{background: red; width:150px; height:150px;}
a{display: inline-block; background: #00FF99; padding:20px; border-bottom:4px solid #00CC00; color:#00CC99; text-decoration:none; margin-bottom:20px;}

$(document).ready(function(){
    $(".büyüt").click(function(){
        $("div").animate({width: "400px"});
    });
    $(".kücült").click(function(){
        $("div").animate({width: "150px"});
    });
});