How to Downgrade iPhone 3GS iOS Firmware from 6.1.6 to 6.1.3 Posted on March 23, 2014 by admin 13 This video will show you how to Downgrade iPhone 3GS iOS Firmware from 6.1.6 to 6.1.3. Share this:FacebookTwitterPinterestLinkedInTumblrRedditTelegramWhatsAppMorePocketEmailLike this:Like Loading...