Nowadays if anybody want to restore their iPhone devices so they must download an iOS firmware IPSW file for iPhone by iTunes or by direct links Below you'll find direct download links to firmware files for all iPhone models. Firmware files available for download on this site are hosted on an Apple..iPhone firmware direct download. Download iPhone iPSW Firmware for all devices here for downgrading or restoring.
The following links are directly to the IPSW files as found on Apple servers.
Here you can Download current and previous versions of iOS Firmware and receive push notifications when new firmwares are released.
You can use IPSW files on Mac or Windows, both require iTunes to work properly. All Your Apple iPhone, iPad, & iPod Touch News. Apple's official firmware release site can be found here, but it may be a bit difficult for the average person to read.