Clean URL's Using OpenCart's Router Class

How do you write clean URL's in OpenCart using their built in Router class? Here is my .htaccess file:

RewriteEngine On
RewriteRule ^(system) - [F,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule .* index.php/$0 [PT,L]

The work is very hard To modify more than 3 files

catalog\controller\common\seo_url.php
catalog\model\tool\seo_url.php

Add this line to your file to modify

$this->load->model('tool/seo_url') and used $this->model_tool_seo_url->rewrite() to rewrite.

Hard to say clearly,the above are only approximate