how to change class name of an element by jquery

<div class="bestAnswerControl">
    <div id="ct100_contentplaceholder_lvanswer_control_divbestanswer"  
         class="IsBestAnswer"></div>
</div>

I want to add:

.bestanswer
{
    // some attribute
}

I want to replace class="IsBestAnswer" of div to class="bestanswer" by jquery. How do I do this?

I am using this approach:

$('.IsBestAnswer').addclass('bestanswer'); 

but it's not working.