assuming u know how to navigate thru your filesystem
using ls - list director contents and cd - change dir etc
change to the directory containing the Xf86config-4 file.
cd /etc/Xf8 (press tab for command completion)
use simple command line text editor pico to edit the file
the commands for pico are shown at the bottom of the editor just look at the structure of the config file and u will see lots of lines are commented out already with a # at the start if i remember right.
Just add a # to the line u want to comment out then press CTRL X
to quit pico .. it will prompt u if u want to save the modified file type Y for yes then ENTER to exit ......
hope that helps