change layout of category page in magento

You can do this either in catalog.xml or in local.xml

I had done following code for local.xml

<?xml version="1.0"?>

<layout version="0.1.0">

   <catalog_category_default translate="label">

    <reference name="root">

        <action method="setTemplate"><template>page/2columns-left.phtml</template></action>

    </reference>

   </catalog_category_default>

</layout>