Depends on the chart type.
If you have a column chart you will need to change it to Bar
If you have a line chart you will need to change it to xy-scatter AND
use work around tricks in order to get category labels on the vertical axis. http://peltiertech.com/Excel/Charts/ArbitraryAxis.html
If it's xy-scatter you will need to alter the ranges used for the x and
y values.