How to Change the Submitted By Text in Drupal 7

In your theme's template.php file,

function YOURTHEME_preprocess_node(&$vars, $hook) {
    $vars['submitted'] = date("n/j/Y", $vars['created']);
}

NOTE: You have to have these other components to get it to work right:

1) In the content type setup:

Make sure the "Display author and date information" option is checked under the "Display settings" tab.

2) In node.tpl.php:

      <?php if($display_submitted){ ?>
          <div class="article-date"><?php print $submitted; ?></div>
      <?php } ?>