To move a single decoration, just move the cursor over the appropriate portion of the decoration to get a move hand:

To move a set of decorations, select them and then move the cursor over the appropriate portion of any one of the selected decorations to get a move hand.

Some decorations are immovable—they cannot be moved.  For example, outlines that indicate image overlap regions after stitching may be resized, but not moved.  If you try to move an immovable decoration, nothing will happen.