Your system and my system specs are very similar, even I had the same problem before.
Download the AMD catalyst control center from Here
If you right click on the desktop and you find two options named 'Graphics Properties' and 'Switchable graphics' (Both with a small red logo) then ignore the download.
1.Right click on desktop and click on 'Graphics Properties'.
2.and then then click on PowerPlay.
then you will get this window
3.Check the checkbox 'Enable PowerPlay'
4.Below the 'Enable PowerPlay option' you can see 'Plugged in:' and 'Battery:', Set both of them on Maximize Performance if you don't want games to be lagging. If you are concerned about the battery then you can set "Battery:' to 'Maximize Battery life' and 'Plugged in:' to 'Maximize Performance'
5. Close the Catalyst control center and then right click on desktop and click on switchable graphics.There you can see the recently played games and beside that a yellow colored box saying 'Not Assigned'.
Click on it and it will change to Red color box saying 'High Performance'.
Click again and it will change to green color box saying 'Power saving'
You can see a screenshot of it below
Actually in Switchable Graphics 'Power saving' means it is using Intel HD Graphics 4000.
and 'High Performance' means it is using ATI Radeon 7670M Graphic card.
If it is in 'Not Assigned' mode then it is using Intel HD Graphics 4000.