Switchable graphics not working for AMD Radeon HD 8850

I have bought a new Dell Inspiron 3537 laptop (Thailand ) and installed windows 8 professional.

Downloaded the AMD catalyst install manger version - 08.00.0911 from the below link :

http://www.dell.com/support/drivers/in/en/indhs1/DriverDetails/Product/inspiron-15-3537?driverId=PWTRP&osCode=W864&fileId=3287401962&languageCode=EN&categoryId=VI

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Installation was successful but I was getting display driver is not enabled error message from catalyst manager. I fixed it by updating the driver from the Device manger and it installed successfully with version : 12.100.14.7000

When I try to switch my AMD APU instead of Intel HD 4000, I do not have any option in the "Switchable graphics" !!

Please guide me on how to fix it ....