You add and remove parameters by moving them between the windows:
- Highlight a parameter in the Category Parameters window and click
(Add Parameter) to move it into the Label Parameters window. - Highlight a parameter in the Label Parameters window and click
(Remove Parameter) to move it into the Category Parameters window.
Labels display their parameters from the first to the last (top to bottom) as listed in the Label Parameters window. You reorder the label by highlighting a parameter and shift its position using 
(Move Parameter Up) and 
(Move Parameter Down).