How to change Wordpress default emoticons

Install the Smilies Themer plugin
Activate it.
Go to Settings > Smilies Themer and pick a theme pack. If you want to create a custom one, keep reading
Create a folder with the name of your theme pack in wp-content/themes/smilies-themer/. In my case I called it devthought
Place your emoticons in that folder and a file called package-config.php

Place a code like this in package-config.php

<?php
 
/*
 * Package-Name: Theme name
 * Package-URI: http://yourwebsite.com
 * Package-Description: Your theme description
 * Package-Author: Your name
 * Package-Author-URI: http://yourwebsite.com
 */
 
$wp_smilies = array(
	'>:o'      => 'angryface.png',
	'>:-O'   => 'angryface.png',
	':-['       => 'blush.png',
	':['         => 'blush.png',
);
// add as many as you want respecting the same format:
// 'emoticon' => 'file.jpg',