From LedHed's Wiki
To transfer the Schema Master role via command line:
Using a command line Open Command Prompt.
Type:
ntdsutil
At the ntdsutil command prompt, type:
roles
At the fsmo maintenance command prompt, type:
connection
At the server connections command prompt, type:
connect to server <DomainController>
At the server connections command prompt, type:
quit
At the fsmo maintenance command prompt, type:
transfer schema master
Reference
https://technet.microsoft.com/en-us/library/cc816645%28v=ws.10%29.aspx