You become root in xterm, then start emelfm2.

Thats only needed to edit files outside your /home/user directory (usually).

If its a file (outside /home/user) that you want to repeatedly edit, then (while your running emelfm2 in root mode), set permissions to allow user to edit the file. Then the next time you can edit it without root permissions. If its an important system file you might not want to give this write permission to user for security reasons... in that case just xterm/sudo gainroot/ and edit each time.