[jQuery] Change the content of a DIV section

[Danjojo]

        <div id="topPromo">
                <p class="centered"><img src="images/top_promo.jpg"></p>
        </div>

How do I go about using Jquery to change the contents of a div?

Sometimes I may want it to be:

        <div id="topPromo">
                <p>Lipsum ernum hoki doki...</p>
        </div>

Other times:

        <div id="topPromo">
                <p class="centered"><img 
src="images/new_product_pictuer.jpg"></p>
        </div>

I have the basics of JQuery going and have done some basic tutorials
like.

$(document).ready(function() {

        // highlights image borders we have specified with the imgBorder
class
        $(".imgBorder").hover(function() {
                $(this).addClass("boldOutline");
        },function(){
                $(this).removeClass("boldOutline");
        });