easiest way is to make them 'floating' on the dashboard.

If you are floating things, you should be able to drag it anywhere.

If you are tiled, you can still drag things around, and the tile layout will re-adjust.  If you are tiled, click on the legend.  It will get outlined in grey.  At the top is a small dotted area (circled in the screen shot below).  Click on that and drag to the bottom.  As long as you continue to keep the mouse clicked, the dashboard editor will highlight grey areas where it will drop the object if you let go.  When you like the greyed area, unclick and tableau will drop it there.

you are welcome. Can you mark this answered if that covered it?