click the "Series Options" icon. There, slide the Series Overlap value to "100%," and change the Gap Width to a value that works well on your chart (your chart will change as you drag the slider).

Which icons you see depends on which part you ... the option to delete and reset individual elements, as well as change the chart type and relaunch the Format Chart Pane for more options.

Plenty of third-party launchers make it possible to change icon sizes, grid layouts, and more. We recommend a few launchers for those who want more control over their icons (and UI, overall).