I have made a graph in libreoffice calc, and in the legend by default the labels are “Column A”, “Column B”, etc… how do I edit the labels?
Let me extend the correct answer of @eldon.dehart a bit.
If you select the data range including the name of the column (or row) of your data, Calc will automatically assign the name. However for this you must set the correct situation in the Chart wizard item DATA RANGE.
However, you can add column (or row) names later. Ideally they are above your column but they also can be somewhere else. To add the column name do:
Double click you chart to see 6 small little black squares around your chart and a grey frame
right click > select Data ranges > Tab Data series
select the series you want to change (left window Data series)and it should contain Column A, B, …)
in the Data range window right > click Name > Click button at right side of Range of names > select a cell (or more) with the name of your column
do above for each column and click OK at the end
I recommend to have a look at the free guides which you can download from http://www.libreoffice.org/get-help/documentation/
it will use the title in the top of the column as the name. I think it is set up with the wizard when you make the chart.
This is definitely the best approach from the point of view of clear data structure in your spreadsheet — If you consider your question as solved, please click the OK button to signal others that in this question is a working solution.