To change the overall visual appearance of this histogram (or any other chart, for that matter), make sure that the chart is selected and then open the Design tab under Chart Tools on the Word ribbon.
Click any image below for a larger view.

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Expanding the Chart Layout options will show several layout designs that can be applied to the histogram. You can widen the width of the columns, move them closer together, and display the value associated with each column among other things.

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Similarly, you can expand the Chart Styles options to see different possibilities you can choose for the color and appearance of the column bars.

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If you’re not sure about which options you want to choose, you can always apply them to see how they will appear on your particular histogram, and then Undo them if you don’t like the result. The screenshot below shows one example of a histogram with a modified layout and style.

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