How to jailbreak iPhone 4s version 6.1.3?

I want to jailbreak my iPhone, version 6.1.3… And I know you can use redsn0w and stuff like that but when I download that to my Mac, when I try to open it, my computer says this app came from an unidentified developer and it can't be open. It has something to do with the system preferences or something, I tried to change it but I can't. I used evasi0n to jailbreak my old phone that's on version 6.0 I think and it worked fine. But evasi0n only goes up to 6.1.2.Is there a different program that I can use that my Mac will let me open? And if not is there a way to downgrade the system on my phone to a 6.1.2?

Http://lmgtfy.com/?q=How+do+I+jailbreck+a+iphone+4+s+version+6.1.3

Was that so hard.