Change to USB camera

Question

I need to take screenshots from webcam to save on my computer. But the webcam is very low quality Please can anyone tell me what should I change to use another webcam I put in a USB port on my laptop, rather than the integrated camera?

    import cv2

    cam = cv2.VideoCapture(0)

    cv2.namedWindow("Python Webcam Screenshot App")

    img_counter = 0

    while True:
          ret, frame = cam.read()

    if not  ret:
          print("failed to grab frame")
          break

    cv2.imshow("test",frame)

    k = cv2.waitKey()

    if k%256 == 27:
       print("Escape hit, closing the app")
       break

    elif k%256 == 32:
        img_name = "opencv_frame{}.png".format(img_counter)
        cv2.imwrite(img_name,frame)
        print("Screenshot taken")
        img_counter+=1


    cam.release()

    cam.destroyAllWindows()