This is how to change the  Security settings on Domain Controller to windows 2008

Click Start, click Run, type gpmc.msc, and then click OK.

In the console tree, right-click Default Domain Controllers Policy in DomainsCurrent Domain NameDefault Domain Controllers Policy

In the Group Policy Management Editor window, in the console tree, go to Computer Policies/Windows Settings/Security Settings

To apply the Group Policy change immediately, either restart the domain controller or open a command prompt, type the following command, and then press ENTER:

gpupdate /force