A simple screenshot below shows you how you can easily enable/disable resource governor. By using SQL Server Management studio, connect to the instance where you need to enable Resource Governor. Then navigate down to Management and expand to see resource governor. There you can simply right click and choose Enable from the pop up menu. You can also enable by using T-SQL by simply passing below command.
ALTER RESOURCE GOVERNOR RECONFIGURE;
To disable via GUI, using your SSMS navigate to the management again and then right click on Resource Governor and choose Disable from the pop-up box. Alternatively, you can pass below T-SQL command to disable.
ALTER RESOURCE GOVERNOR DISABLE;