You can effectively merge multiple items into one. Merging makes sure you can remove duplicated items; when you have multiple items created, which are essentially one and the same, you can change them to one target item. This is true for property items as well as any module that is a sub-module (such as actors, music artists, etc).
Simply select the duplicated items in the view, right-click and select Merge from the pop-up menu.
A very simple window is opened. The only thing you need to do here is to choose the target item. This is the item to which the previously selected items will be merged.
Press Apply and the process will be started. You can follow the progress in the log overview located in the lower part of the screen.
When the items are merged only the target item remains.