To let WSUS to upgrade (and not update) the Windows 10 clients you need to:
1- Install this update if not already installed : KB 3095113 (http://blogs.technet.com/b/wsus/archive/2015/12/04/important-update-for-wsus-4-0-kb-3095113.aspx)
2- Add the .esd – application/octet-stream mime type on the iis server of the wsus server :
This happens when upgrading from Windows 2008 or higher to another version of Windows.To solve the issue open ADSI Edit and change the value on the following path:
CN=CA,CN=Enrollment Services,CN=Public Key Services,CN=Services,CN=Configuration,DC=domain,DC=domain
The key to change is the “flags” and must be put to “10” (it’s easy to find it as “2”).
After that restart the CA service.
1- Demote the DC using the dcpromo /forceremoval.
2- Remove the server from the PDC using Active Directory Users and Computers, flagging the “this domain controller is pemanently offline and can no longer be demoted using the active directory domain services installation wizard (DCPROMO)” checkbox. It is not necessary to clean with ntdsutil the metadata. These operations are included with the deletion of the domain controller from the GUI.
3- Remove the AD role.
4- Reinstall the AD role.
5- Promote the DC using dcpromo