How to update ios 5.0.1 iphone 4 to ios 6.1.2 after release of ios 6.1.3?

I've heard that i shouldn't update to ios 6.1.3 if i want to jailbreak my iphone so i want to update to ios 6.1.2 but itunes won't let me. I already know how to jailbreak and all but i just couldn't figure out how i can update to 6.1.2.

I've had this similar problem, sorry I'm not sure what to do.

You can't update to 6.1.2 any longer since 6.1.3 is out.
Itunes checks the update and it doesn't allow older versions to be installed.

This is actually quite simple. If you have a method of jailbreaking your iOS 6.1.2 all you need to do is find the 6.1.2 ipsw file online for your respective device.

Once you have this file, hold Shift and click restore in iTunes, this will prompt you to browse for your ipsw file that you just downloaded. Now restore your device with that file and woolah! You'll be running 6.1.2

You can find the ipsw file on one of the download links here: that direct you to redmondpie.com's files:
http://infiniteinstructions.com/ios-613-jailbreak-on-pre-a5-iphone-and-ipod-touch-using-redsn0w.html