1. Log-in as Admin and choose Structure, Content types and click edit (under Operations) for the corresponding content type (e.g. Article).
2. Click Display Settings and un-check Display author and date information check box.
3. Save settings by clicking the Save Content Type button.

1. Enable Display Settings for the corresponding content type.
2. Edit the node.tpl.php file of the corresponding theme you are using, e.g. themes\bartik\templates\node.tpl.php and located the following command:
print $submitted;

3. Now replace this command with the following code:
// print $submitted;
if ($submitted) {
echo "Posted: " . date( "F j, Y",$node->created);
}

4. Save the file and you should see the submitted information in the desired format. Of course, you can use a different date format or add additional node details.