Never heard of the Matrix control panel, but you can use any text editor that you have on your machine. vi, Emacs, pico, nano, joe, gedit, etc will be fine. Open up a terminal window and "become" root using the su command and entering your password, then enter the name of the editor you want to use followed by the path to the file, e.g.
$ su
<password>
# emacs /path/to/httpd.conf
If you're using Ubuntu or something that uses sudo, then I believe you'd just need to use
$ sudo emacs /path/to/httpd.conf
