When you remove a category from an app, any other applications to which you assigned the category retain the assignment. Deleting or removing a category does not remove any applications from the list on the My Apps page.
To remove a category:
On My Apps, switch to the details view:
On the application's row, click the X icon in the Category column. The category is removed from that app only.
Note: When you remove the category from the last app to which it is assigned, the category is deleted.