You can acquire "Character Cards" through various methods such as shop purchases or by opening bags.

If you obtain a Character Card for a character you don’t own, you can equip that character. As you collect more Character Cards, you can use them to upgrade the character’s abilities.

To change or upgrade your character, go to the [Locker Room] menu at the bottom of the main screen. As the character’s level increases, more Character Cards will be required for further upgrades.