So from the very beginning :

1) Mount downloaded ISO from the site below:
http://sourceforge.net/projects/nethserver/files/nethserver-6.7-x86_64.iso/download

2) Please see the login credentials.

User name: root
Default password: Nethesis,1234

3) Use default credentials to log in.

RESET ROOT PASSWORD PROCEDURE

1) Reset VM or Server and press any key.Than Press "e" to edit.

2) Press "e" to edit KERNEL parametr.

3) Add init=/bin/bash at the end of the line and press ENTER. Finnaly press "b" to boot

4) Next run mount to make sure that / file system is rw , if not run mount -n -o remount,rw /
5) Run passwd to change root password.

6) Reboot VM or Server.