The only way I've found to do this is to reduce the amount of space that the chart itself takes up within the whole box, you can do this by ensuring you have focus on that chart (single click in the caption area) then press CTRL-SHIFT and hold that combination down. When you do this you will see red lines around the chart areas, you can then grab the bottom of the chart area and drag it up, therefore providing more room for the axis labels to fit in.
You can reduce the label length by going into the presentation tab of the chart properties window and then select the limit legends check box and then specify the number of character you need to present in the axis of the chart. Even after doing this if you are not able to get the chart right, increase the height and width of the chart and then press Contol+Shift and increase the chart size by dragging it down. I hope tis helps you and you will get to your solution.