aspire v 15 using only intel hd graphics not nvidias

So i have   aspire v 15

• 16 GB DDR3L SDRAM │ 1 TB HDD │ Windows 8.1 64 bit│ Intel Core
• i7-4510U processor (4 MB cache) up to 3.1 GHz turbo speed│ NVIDIA GeForce 840M
• Graphics with 2 GB Dedicated Memory
• 5000 mAh 6-cell battery providing up to 7 hours of run time │IEEE
• 802.11a/b/g/n wireless internet │ HDMI port, 2 USB 2.0 and 1 USB 3.0 Ports, VGA,
• and Network (RJ-45) port
• 15.6" Full HD LCD (1920 x 1080) 16:9 with Acer

 and it only using intel hd graphics for some reason i change everything in nvidia control panel to nvidia  high speed processor and it  still doesnt work