Gradebook

I have created a Category in the gradebook with the Natural weighting option. I would like to be able to change the Grade type to Scale under the Category total as shown in the documentation https://docs.moodle.org/28/en/Grade_categories#Editing_a_grade_category However, when I hover my mouse over the Grade type all I get is a gray circle with a slash indicating that I cannot interact with that dropdown. Is it not possible to change the Grade type on a Category total or is there an Admin setting that I missed to allow this? We are running Moodle 2.8. Thanks.