Sorting grouped bar chart by numeric value?

Dear all,

I have created a bar chart where the average sales per manufacturer for the years 2014 and 2015 are shown next to each other in a bar chart. I would like the manufacturers now being sorted according to the highest average sales in 2015. However I do not seem to be able to change the sorting and they are always displayed in alphabetical order. If I just pick one year the sorting is fine but if ad the second year to the bar chart the change to alphabetical sorting appears. What can I do?

Thank you

Jörg