/etc/X11/xorg.conf

How do I get in /etc/X11/xorg.conf to add lines?

If you don’t know how to edit it. Are you sure you know what you are going to add/edit?

kde:

kdesu kwrite /etc/X11/xorg.conf

gnome:

gnomesu gedit /etc/X11/xorg.conf

When open go to save as and call xorg_backup.conf
Then close.

Re open xorg.conf

If you have an NVIDIA card, you can use nvidia-config but for any Xorg.conf changes to “take” you need to run it as root.