How can I switch from Intel onboard grpahics to Nvidia Dedicated GPU?

When I go to windows screen resolution I see intel. I cant change it.

I go to Device Manager, I see both Adapters are there and Nvidia is known.I disabled intel, I didnt see any option to set one as primary so I disabled intel, black screen!Reboot and re-enable intel.

I right click on the desktop, choose "Nvidia Control Panel" and on 3D options I chose the desired game I want to play, High performance Nvidia, but it didnt switch when I started the game.

Then I made preferred GPU in the global settings High performance Nvidia for everything it still didnt change.I understand to save the battery etc. there is a switch option between these two but I dont see this switch when it is necessary, I cant also switch manually?Is there a manual switch FN key?I looked but couldnt find.

Why I want to do this?

1) Better game peformance.

2) I want to play an old game from 2002(Diablo 2 LOD), when I start the game there are black bars on the sides, so screen becomes just smaller which I dislike!I heard this is intel's specification to center the display.But instead I would like to scale or expand it to fit widescreen(fullscreen).Which should be possible with Nvidia.

My Notebook Specs: Fujitsu Lifebook AH531, Win7 , 64 bit, i5, intel HD graphics onboard, Nvidia GT 525.

I didnt install Nvidia later, it was always installed and ready from the moment I turned on the computer first time.

How I determined that the cards werent switched when I am playing the game: with the windows key I exited from the game, then looked at screen resolutions menu, still saw intel, also the game was still with black bars.I know intel GPU should enough for Diablo 2 but I am interested in this answer for further games, I dont always play Diablo, what if I install an up to date game for example?Then Intel will not be sufficient.I would like to learn the switch option.