Transfer or seize FSMO roles

ntdsutil
roles 
connections 
connect to server <FQDN of role holder>
quit 
seize schema master
seize naming master
seize RID master
seize PDC
seize infrastructure master
quit 
quit 

Use transfer keyword instead of the seize keyword, if the old DC is accessible

Open Active Directory Sites and Services, expand tree <site name> \ Servers \ <server name>

Open properties on NTDS Settings, and remove the tick from 'Global catalog' checkbox