Rerse

Method 1

Use Plugin

1. postMash – custom post order
2. Custom Post Order

Method 2

Edit index.php of the current theme

Place this code

<?php query_posts($query_string . '&orderby=modified&order=desc'); ?>

before

<?php if (have_posts()) : ?>

References

1. http://codex.wordpress.org/Template_Tags/query_posts
2. http://perishablepress.com/press/2008/01/22/6-ways-to-customize-wordpress-post-order/
3. http://forum.bytesforall.com/showthread.php?t=3063