Will restore from backup change my iOS?

No. The back up does not contain the operating system. Unfortunately the backup files only contain personal data, and don’t store the iOS version. Apple makes very difficult, if not impossible, in some cases, to downgrade iOS versions.

Does resetting iPhone change iOS version?

1 Answer. Erasing All Contents and Settings (what most people call “factory reset”) does not change/remove your operating system. Whatever OS you had installed prior to the reset will remain after your iPhone reboots.