How to change category page layout in Magento

Default Category page layout is written in page.xml file which resides in app/design/frontend/default/your-theme/layout/. Open Page.xml then change line number 35 or find .

<default translate="label" module="page">

<label>All Pages</label>

<block type="page/html" name="root" output="toHtml" template="page/3columns.phtml">


Change default 3columns.phtml to 1Coloumn.phtml or 2columns-left/right.phtml .Then save and upload it .
Clear your cache to see the effects.

Note :: Changing all page layout doesn't effect other pages of magento it effects only the category page. So don't hesitate to change this.