1. If you have downloaded the firmware of the corresponding model (it is not recommended to use iTunes to directly detect the update and upgrade, because downloading firmware with iTunes is very slow), you can log on to the website of the synchronization assistant to download it.

2. Update iTunes to the latest version (select "Check for updates" in the iTunes Help menu).

3. Run iTunes and connect the device, and click the icon in the upper left corner to enter the device summary page.

5. Then press and hold shift on the keyboard, click the Update or Restore button on the iTunes interface, and then select the corresponding version of firmware to upgrade.

What needs to be emphasized here is that shift+ update only upgrades the system, and the data on the device is generally not erased, but please make a backup of the data just in case.

Shift+ recovery is equivalent to brushing the machine, the data on the device will be emptied and the system will be purer.

6. Upgrade successfully, and then follow the prompts to activate on the device to experience the brand-new system.