1. Navigate to the "Calendar" from the main menu on the left.
  2. Click the "Categories" button.
  3. Locate the category that you wish to edit and  click the blue "Edit" icon to the left of the entry.
  4. Use the "Category Editor" to make any necessary changes. 
  5. When finished, click "Save". 

This will only affect the category events scheduled after the changes have been saved.