To change the Picture settings of Elgato Game Capture HD, first select Capture mode.

Then, press the Settings button in the Device section of Elgato Game Capture HD.



The Settings button has a hammer and wrench icon on it.

   
Under Picture, use the sliders to change the Brightness, Contrast, Saturation and Hue.

If you don't like the changes you made, you can use the Reset Defaults button at the bottom, left corner of the window.