The viewing grid consists of cells. Each cell may contain one Item. The default aspect ratio of a cell is 16:9 but it can be changed (see "Changing Cell Aspect Ratio").
In order to move an Item, Click on it and Drag it to a new position (grid cell borders are visible while in motion).
If the desired position is already occupied, Items will be swapped (if possible).
If swapping is not possible, the target cell will be marked red:
If bigger Item is being replaced by a smaller one, they will swap sizes as well as positions.
You can also use a right-click to move all Items in the Layout as one.