To increase your pirate's star, you have to follow these requirements first.
- A pirate must reach the maximum level.
- Extra pirates for sacrificial or Promotional Bird with the same star rating or higher.
- A certain amount of Rum.
Here is the step by step procedure on how to promote a pirate:
1. Go to Training Grounds in your Hideout
2. Tap on "Promotion"
3. Tap on the pirate that you want to promote.
4. Then tap on the pirates or Promotional Bird that you will sacrifice
5. Tap "Evolution"
After this process, the pirate's rarity and the maximum stats value will increase and the pirate level will be back to level 1. You will not be able to use unlocked passive skills that have been available at a higher level, however, it can be unlocked when you reach the required level again.