Select the chart
Click the Layout tab under Chart Tools.
Click Chart Titles button
Click 'None' to hide the chart title.
Click 'Centered Overlay Title' to insert a title on the chart without resizing it.
Click 'Above Chart' to position the chart title at the top of the chart and resize it.
Click More Title Options to set custom chart title options.
Double-click the text box to place the insertion point
Then modify the text.