How can I edit the /etc/ssh/ssh_config file? I tried editing the /etc/ssh/ssh_config file on my Mac to change the forwardX11 from no to yes, and this to enable X11 features.

I try to change permission in the file ssh_config and in the folder etc, I did it, but in vain; still no permission to go inside the file to change something.
I find the answer, with this line in Terminal :

sudo nano -w /etc/ssh/ssh_config