An operating method of an electronic device including controllers includes updating, by a first-level controller of the controllers, a first-level firmware of the the first-level controller, writing, by the first-level controller, a second-level firmware to one of second-level controllers of the controllers having a lower level than the first-level controller, booting, by the one of the second-level controllers, by performing a reset operation, verifying, by the first-level controller or the booted second-level controller, whether there is a target second-level controller with out-of-date firmware, and writing, by the first-level controller or the booted second-level controller in response to a result of the verifying, the second-level firmware to the target second-level controller.