in the bar chart, how to re-arrange the sequence of wave?

Take the attached chart as example, I need to make back bars on the right to the whit bar in each category.

many thanks
Screen Shot 2015-01-19 at 10.24.59.jpg (46.62 KB)
You need to select Graph>Reorder Traces. The trace names in the small dialog box that opens can be dragged around to reorder them.