If you've been following along in this tutorial, you can probably guess how to format the legend. But in case this is your first stop, here goes:
Press Control on the keyboard and click on the legend (remember: the legend is on the Chart Area, so be sure the cursor says Legend (hover for a second) as oppsed to Chart Area, otherwise you will not get the menu options you need). You can tell when the Legend is selected because blue dots appear on the corner. Select Format Legend from the dropdown menu.
This will open the Format Legend dialogue box.
Alternatively, you can reach this dialogue box by going to the Format tab under the Charts toolbar and selecting Legend from the dropdown menu found at the top of the Current Selection group (far left of the Ribbon). Then select Format Selection.
You can also select Legend Options from the Legends section of the Labels menu of the Charts Layout tab (or select one of the options for moving the legend).
The quickest way to open the Format Legend dialogue box is to double click on the legend.
Under Legend Placement in the Format Legend dialogue box, you can change the legend position by clicking on the preferred location. You can also let the legend overlap the plot area by unchecking the box next to Show the legend without overlapping the chart. Additionally, all kinds of visual changes can be made in Font, Fill, Line, Shadow, Glow and Soft Edges, but there's no 3-D Format for the legend. Use your own discretion when experimenting with these features.
You can resize the legend with your mouse just like you can with the chart.
Finally, to alter the font size, style, or type, click on the legend and use the options in the Font group under the Home tab, just like you would with the chart title. You can't alter the text like you can with the chart and axes titles. To change the text in the legend you need to right click and go to Select Data and edit the series name.