This Blog describes how to change the server authentication mode in SQL Server 2012 by using the SQL Server Management Studio or Transact-SQL. During installation, SQL Server Database Engine is set to either Windows Authentication mode or SQL Server and Windows Authentication mode. After installation, we can change the authentication mode at any time.
To change the security authentication mode follow the steps given below:
In SQL Server Management Studio Object Explorer, right-click the server, and then click Properties.
On the Security page, under Server authentication, select the new server authentication mode, and then click OK.
In the SQL Server Management Studio dialog box, click OK to acknowledge the requirement to restart the SQL Server.
In Object Explorer, right-click your server, and then click Restart. If the SQL Server Agent is running, it must also be restarted.