You can disable your less-powerful video card in Windows Device Manager. You can usually get to the device manager by holding the Windows key and pressing the “Pause/Break” key. Then click “Device Manager” on the left-hand side. In Device Manager, your video cards will be under “Display Adapters”. Right-click the one you want to disable, and press “Disable.”
If your video card has a tool that lets you adjust performance settings, you can set your video card to be the one to be used by specific programs. For instance, in the NVIDIA Control Panel, you may be able to tell Superfight to use your NVIDIA video card with the “Manage 3D Settings” submenu. Under the “Program Settings” tab, you can select a program to customize.