You can do without losing any data ( take a backup in case anyway).
1. Download 10.3.1 ipsw ( seacrh online)
2. Open itunes, connect iphone, clck on Shift+ update ( windows) select ipsw.
3. Phone will be downgraded to 10.3.1 and all data will be intact.
I've done it numerous times too, but its all chalked up to YMMV. I've had instances with no problems, and then I have instances where everything went to hell in a hand basket. For peace of mind sake, its easier to DFU.
I've done it numerous times too, but its all chalked up to YMMV. I've had instances with no problems, and then I have instances where everything went to hell in a hand basket. For peace of mind sake, its easier to DFU.
You can't restore your backup from a higher version of iOS to a lower version unless you edit the backup file, which could be catastrophic. Simply restoring your backup does not downgrade your OS.