Oh wait, I actually did change settings of the SSH server to allow "root" to login, since I need access to all the Linux files and system configurations spread around in /etc e.g.
(Lines below assume you are logged directly into the console of the Linux machine using user "root".)
I set..
PermitRootLogin YES
in..
/etc/ssh/sshd_config
You can edit this config with..
nano /etc/ssh/sshd_config
Use CTRL+S to save and CTRL+X to exit "nano" editor.
Then reboot or restart the ssh-daemon..
systemctl restart sshd
Then connect / browse the SFTP connection to that server with DO at file system root ("/").