2. Back up telephone address books, photo albums, voice memos, etc. You can view it in phone settings -iCloud. As long as all functions can be turned on, the corresponding program file information can be backed up after turning on.
3. After the upgrade, log in to the mobile phone with the same appleID account, turn on the iCloud synchronization function, and download all the information backed up before. Note that you need to connect to the network when synchronizing.