data->capture =cvCaptureFromCAM(data->config.device); // open the device
...
IplImage *grabFrame=cvQueryFrame(data->capture);

cvSetCaptureProperty(data->capture,CV_CAP_PROP_FRAME_WIDTH,1920);
cvSetCaptureProperty(data->capture,CV_CAP_PROP_FRAME_HEIGHT,1080);

The function cvSetCaptureProperty() sets the specified property of video capturing.
Currently the function supports only video files: CV_CAP_PROP_POS_MSEC, CV_CAP_PROP_POS_FRAMES, CV_CAP_PROP_POS_AVI_RATIO.

static const int MAX_WIDTH_RESOLUTION = 7680;
static const int MAX_HEIGHT_RESOLUTION = 4800;

cvCreateCameraCapture(...);
cvSetCaptureProperty(pCam, CV_CAP_PROP_FRAME_WIDTH, MAX_WIDTH_RESOLUTION);
cvSetCaptureProperty(pCam, CV_CAP_PROP_FRAME_HEIGHT, MAX_HEIGHT_RESOLUTION);
cvQueryFrame(...);