well you navigate just like any other Linux box
you will also need to know an editor that is installed on the linux box, and will launch form the CLI - like vi, nano, whatever. That's a function of what is installed or - if its your box or a VPS, what you add in the way of editors.
when you are done editing, be careful of ownerships and permissions, they can break LAMPP.
That file is found in /opt/lampp/etc/extra
here's where to find things (down by the bottom)http://www.apachefriends.org/en/xampp-linux.html
Don't laugh about the 'remote' comment - I have had people trying to FTP into the box they are actually on... "I thought you had to upload via FTP" "well, yes UNLESS you are actually ON the machine" -
If its YOUR linux server or a VPS you may want to learn about Webmin.