I have a jailbroken and unlocked iPhone 3Gs on iOS 5.0.1. It is unlocked with ultasn0w and its baseband is 5.13.04. I want to update it to iOS 6.1.3 without updating the baseband. I know how to do it with sn0wbreeze, but the only problem is that I have a macbook pro. I tried using redsn0w, but an unexpected error occurred. Please help me.