Using the Sample superstore as a reference:
1) Let's plot a bar chart showing SUM(Quantity) for each Segment:
2) Right click on the x-axis (Segment):
Notice we don't have an option to edit the axis, only header. This is because only continous values form the AXIS.
3) Similarly, right click on the y-axis (Quantity):

Now we have the option to edit BOTH the axis and the header.