You cannot switch ON or OFF the Infrared night vision manually.
Night vision will automatically be switched on when it gets dark, and switched off when there is sufficient light again.
Note ! : When you experience problems with the picture quality in the dark, then you probably have pointed the camera to a white wall/ceiling. Make sure that you point the camera in a different direction and make sure that the camera is more than 30 to 40 cm removed from the wall/ceiling. A reflective surface, like a window also causes these issues.