Just give your carryon rolling bags to the porter at embarkation, just costs a tip. Then have a small tote or drawstring bag with swim gear to change into to carry on board. You'll have your suitcase before dinner, if you want to change earlier you still have your clothes you wore onto the ship, if you need them in your tote to change back into. You can always change in a bathroom, or I've heard sometimes the spa will let you change there (but no 1st hand experience).