: Hold the Shift key and click the Restore iPhone (or Update) button.
: A file browser will open; select the .ipsw file you downloaded. Download iOS firmwares
Once you have the file, you can manually "flash" it to your device using a computer: : Hold the Shift key and click the
: A comprehensive database that lists firmware for virtually every Apple device, including niche versions and detailed build numbers. Download iOS firmwares
: The most popular third-party repository. It provides a clean interface to select your device type (iPhone, iPad, etc.) and specific model to find both currently "signed" (authorized by Apple for installation) and "unsigned" (archival only) firmware versions.