When you create a new hub you must assign a category to it. You can go back and change this category later if you wish.
To change the category for a hub you must first open up the hub for editing. Once in editing mode you will see the tools in the right column of the page.
Underneath the "Add More Capsules" tool, you will see a line of links that read:
reorder tags settings summary group
Click on the settings link and another module will open up underneath. The top section will be labeled Category and will display the current category. To change the category click on the link for the category and make your change.