1 How to edit the config.txt?
There are two different way how the config.txt is edited. One is via SSH and the other is by plugging the SD-card to another PC (Windows, Linux or MacOS).
1.1 The SSH way
As LibreELEC's system is generally a read-only system by default, you will need to get those write-permissions first:
mount -o remount,rw /flash
'Nano' is a very easy-to-use built-in text editor:
nano /flash/config.txt
To save the changes you made, press CTRL + o and save the file.
Press ENTER to confirm the existing filename.
To exit the nano editor, press CTRL + x.
Now you have to change back the read/write permissions of the system partition to 'read-only' again:
mount -o remount,ro /flash
You need to reboot for the changes in the config.txt to take effect:
reboot