Upgrading promo tickets from 2-parks to 3-parks

[lubu]

Hello,
I booked a vacation package for next week from Costo Trave, it includes 2-day 2-park tickets and gets extra 2 free days as promotion.
With weather forecasting temperatures to be in the upper 80s for most of next week, we would like to upgrade the tickets to 3-park for Volcano Bay. Is this possible? If so, any idea on how much I would need to pay?

Thanks!