You use an editor. Any editor will do.
I prefer Emacs. Just start console(terminal) and type:
<your root password here>
find / -name lilo.conf
This will produce a result in form like: /boot/lilo.conf
Then all you have to do is :
emacs /boot/lilo.conf (or the path you will get from the find command)
This should open the file in emacs.
Just edit it the way you want.
When you are finished:
press CTRL+X+S (this saves the file, hold CTRL, press X, then press S)
press CTRL+X+C (this closes emacs, hold CTRL, press X, then press C)
This should do the trick.
I don't really know how lilo works, as I am using GRUB, but running lilo should do it, I think.
In console type:
That should do the trick.
Reboot. Good luck