Yawcam -> Preview
The preview window shows the image data pulled from your video capture device.
You open the preview window by clicking "Window -> Preview" in the text menu in the main window.
Usually you can change the update interval of the image in the native driver settings for the device. Look at "Settings -> Device -> Format control" and see if you can change the fps (Frames Per Second) settings there.
The preview window can put a rather high CPU load on some computers if the fps is high, and the image size large. If this is a problem for you, remember to close the preview window when you not are using it.