This assumes you are in a Dock Level below the main, starting level and that the image in the
Centre Button position is not the Circle Dock Centre Button Image.
To move an item up a level, simply drag that item to the Centre Button (ie that level's Dock
Folder) and drop it.
Note that if you are already at the main, starting level, dropping an Item on the Centre Button will
remove that Item from the Dock but, because this could be not what you want, your permission is
asked before removing the Item.