For Azure Stack Hub, this process is described Here. In the event of major hardware issues, the entire Azure Stack Hub deployment can be brought down and then re-started.
For Azure Stack HCI you can find this process Here.
Azure Stack Edge comes as prebuilt hardware, and the update process will take care of all updates. If hardware issues occur, support will guide you through troubleshooting & replacing a device.
Please let me know if you have any other questions.