To move a preset within gallery, select and drag it with your mouse to the left or right part of another preset of a current presets sequence. Dragging a preset to the left part means that you want to place the current preset on the left of another preset, dragging to the right part means that you're going to place the preset on the right of another preset. When dragging the preset over another one, the left or right side of another preset's thumbnail is highlighted showing you the side where the dragged preset will be placed to.
Also you can move preset from one gallery to another. To do this, simply drag it with your mouse over a name of a needed gallery in the Galleries list. The preset will be moved to the end of this gallery. To copy a preset to another gallery, hold the Ctrl key when dragging. In this case, there will be a '+' sign on the preset's icon when you drag this preset over the Galleries list.