here are the steps that may be followed:

1. Connect to the FTP server of your site.
2. Retrieve the file that has to be modified.
3. Modify it.
4. Retransfer it by crushing the ancient same file.

requirements:

> you'll have to know the 'File Transfer Protocol' commands.
> you'll have to know how to manipulate sockets in mirc.

hope this helps you.