Once you insert a chart in PowerPoint, you may find that you mixed up the series and categories! It’s easy to switch between both of them by clicking the Switch Row/Column button on the Chart Tools Design tab of the Ribbon–but wait, do you see the Switch Row/Column button grayed out, as shown highlighted in red within the screenshot below?
The solution is simple, although not so apparent. All you need to do is to right-click the chart on your slide to bring up the contextual menu, shown below. Now select the Edit Data option.
Now PowerPoint will bring up an instance of Excel and open your data, ready for editing. Of course, even if you do not want to edit, you will be happy to discover that the Switch Row/Column button is no longer grayed out, as shown in the screenshot below!