Key entries can be reordered only when the key layout is set to Single Column. The layout can temporarily be set to Single Column in order to reorder entries. When changing layouts the placing of entries into columns always occurs in the same way so that predicting which column an entry will be in is possible.
The reordering occurs as follows;-
Click down on the entry to be moved and then, whilst the button is still down, move the mouse to drag the entry to a new position.
Release the mouse button to finish dragging.
Alternative sources of explanation: