Game objects have an order in the display list of the scene. The order is the index of the game object in the display list. The game object with the lowest index is the first to render, and the game object with the highest index is the last to render. In the Outline view of the Scene Editor, the last object in the display list is stacked at the top of the Outline view.
You can change the order of the objects by using the sorting commands. You can execute them context menu. Select the objects, right click, and select the Edit submenu:
Look it shows the keyboard shortcuts for each command.
In addition you can execute the commands in the tools panel:
