Updating custom firmware in itunes
Some people on a lower firmware should also upgrade to i OS 10.2, but not everyone. If you have an i Phone 7 or i Phone 7 Plus and are on lower than i OS 10.2, do not update to i OS 10.2, stay on a lower firmware!In this guide, we’ll talk you through how to upgrade/downgrade to i OS 10.2 from a lower/higher firmware, if you are one of the people who should be there. Everyone else should check out my advice for all devices on all firmwares to find out if you need to stay where you are, or move to i OS 10.2. You can then add or remove custom versions of i OS software, such as developer previews.
It will not be downgrade since the device itself has IOs 4.2.1 installed.
EDIT: Editing because this no longer works and it gets downvoted by people who didn't read the comments.
Apple wants us to use the latest version, and develop for the latest version, there is no way of downgrading anymore.
Everyone on i OS 10.2.1 or i OS 10.3 beta who wants to jailbreak, now or in the future. 1) Ensure you have backed up your device to i Tunes and/or i Cloud before beginning.
I backup to i Tunes with ‘Encrypt Backup’ selected, to make sure I have a hard copy on my computer which also contains all my app passwords and email account details.