If you check your taskbar icons (next to the Windows clock), you should see an NVidia logo. Right-click it, and choose NVidia GEForce Control Panel (from memory, it's the second item).
In the window that opens, choose "Manage 3D settings" on the lefthand side.
You will now be presented with a window that allows you to customize:
- Global settings (first tab) - These are the default settings that NVidia will apply.
- Custom settings per .exe (second tab) - Here, you can define specific configurations.
For some reason, some games (in my case XCom) tend to favor the Intel HD Graphics. If you add your game's .exe to the list of custom settings, you can force it to use the NVidia card. (You can configure a lot more detailed options than just which card to use, but I'll leave that up to you to find out what you want to do with it. I usually just pick the correct card and do the rest of the configuration from in-game)
Sadly, I can't provide you with screenshots as I don't have my NVidia laptop with me at work.
Good tip: When adding an item, you will be shown a suggestion list comprised of the .exe processes you recently started. I tend to always start the game once (to test performance), close it, then go to the Nvidia menu. Every time, the correct .exe is the top suggestion because it's the last program I opened.