Categories and Sub Categories

Categories and Sub Categories

Hello.

I'm trying to find a way to change the Categories and Subcategories in Desk. I'm unable to find a way to change, add, or remove anything. When we create a new department we might need to add a few other fields to fit the inquiry user contact us about. 

We have this visible in Field Dependencies when all is linked correctly, however, how can I change or add new categories or subcategories?   On the attachment, where can this be changed? I tried to look everywhere but only find something under knowledgebase but, this is not what Im looking for.

Please advice.