A chart is nothing more than a graph of different numbers and data without a legend. A legend tells the reader what each section of the graph is. Microsoft Excel automatically generates a legend with each chart you create, so you don't need to worry about figuring it out for yourself. However, if you're not satisfied with the order that Excel puts the legend in, you can change it.
Right-click on one of the names listed on your legend.
Click on the "Select Data" option from the list that appears.
Click on the entry you want to move in the "Legend Entries (Series)" box.
Click the "Up" or "Down" arrows in the box to change the position of the legend. Click "OK" when finished to save your changes.
For organization and readability, you may want to leave your legend in a reasonable order, such as chronological or highest to lowest.