iOS 6.1.3 (build 10B329) is an official Apple over-the-air update for the iPhone 4 (GSM). The update package is 17.43 MB. This is a delta (partial) update that requires 6.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 71ab4f84fc5a6fcfec2bb5f19b8f086ed9f78ed2.zip.