The word “capsize” is usually restricted to objects that are in water. Boats and ships capsize. When this happens, they turn upside down. “Overturn” can be used with objects that are in water or on land. Lorries, buses, and cars can only overturn; they cannot capsize. The word “overturn” suggests that the vehicle has turned upside down. It can also mean that it is lying on its side. Objects such a shelf or a chair can be overturned as well. So can ships and boats. But you cannot talk about a shelf capsizing. Here are a few examples.
*The ship capsized killing the crew on board. *The students overturned the box and pulled out all the books.