WordPress.org

1. Download and extract custom-smilies.zip; then, upload init.php and custom-smilies.php to the /wp-content/plugins/custom-smilies directory. Upload smilies folder to the /wp-includes/images directory.
2. Activate Custom Smilies in your Admin Panel
3. Put your smilies in smilies folder (wp-includes/images/smilies/)
4. Change the emoticons by navigating to Manage > Smilies and complete the form

Advanced use: Click here to read my blog post