Hi Siungu,
You would probably get a lot more help if you created a new thread. This one is old and will not show up on the top of the list.
One approach that you might take is to try to modify the camera attributes. You can use the IMAQdx Enumerate Camera Attributes VI so that it will return to you the available attributes that can be altered. You will probably need to alter a property that sounds something like "camera mode". To actually alter this attribute, use the Set Attribute VI. This attribute probably has an enum associated with it that will give you options for resolution and speed, so if you right-click on the input of the property node and select create constant, you will make an enum constant that you can use to select the correct setting.
Jeremy P.
Applications Engineer
National Instruments