Changing the number of classes in the Counts and Amounts (Color) style is not honored.

Workaround

1. Add content to ArcGIS Online.
2. In Contents, click the Change Style icon.
3. Select Counts and Amounts (Color).
4. Check Classify Data.
5. Change the amount of classes to other than four.
6. In the Divided By drop-down menu, choose another class to divide the data by. The amount of classes changes.
7. Switch the Divided By drop-down menu to None.
8. Click OK. Changes made to number of classes are honoured.

Steps to Reproduce