Upgrading the Heroes requires Esper, the second currency in Fableborne. To upgrade your Heroes, you'll need to collect enough Esper by leveling up, claiming your Daily Bonus, or successfully defending in battles. Once you've gathered the required amount of Esper, you can navigate to the Hero's profile and select the upgrade option. The process will enhance your Hero's abilities and make them stronger in raids. For specific details on each Hero's upgrade requirements and benefits, please consult the in-game guide or join our Discord community for additional support and insights!