change from additional domain controller to domain controller

[keysteal]

Hello,

question is simple but there is no documentation (official and not) about that. I did my QNAP as additional domain controller of
a WIndows Domain Controller (about that, why in the official documents is not written that Windows Server the functionality
must be set as a Windows 2008 R2 server????? I went crazy to find it in internet). Next step was migrate all roles from
master domain controller to my QNAP, and next demote WIndows domain controller so my QNAP became the primary.
Small detail: my QNAP is pointing as additional domain controller to the old Windows DC DNS, and there is no way to change it
(and if you do it, you loose the functionality of Domain Controller). I've tried to change from additional domain to domain controller,
but it returns an error, and again I loose DC functionality. I've not tried to make changes into Qnap DNS parameters, removing every
pointing to primary DC, before try to change from additional domain controller to domain controller, or simply changing IP of DNS.

Any illuminating reply is appreciated. Thank you