On this website I had nodes that were "story" node types and "blog" node types. It was getting confusing. So I moved all "blog" nodes to "story" nodes by creating a page and running the following PHP code from a Drupal node:
<?php
node_type_update_nodes('blog', 'story');
?>
Steps:
1. Create a new page: node/add/page.
2. Insert code above. "blog" nodes will be changed to "story" nodes.
3. Set "PHP code" as the "Input format".
4. Preview the page.
5. All blog posts should now be converted to story posts.
Quick and easy.