First of all, please make sure your plan is setup for using the grid.

Select the stand(s) you would like to move, you should see Red nodes appear on the corners of the stands as shown below.

If the corner nodes are Blue, press the Space bar on your keyboard to toggle them back to Red nodes.

Select a Red corner node, preferably one that is not next to another node to make it easier for you to select.

Now just move your mouse to a new Grid position and click.

If your mouse is not snapping to the grid points, press F7 on your keyboard. If that does not work, please check your Grid Settings.