If you are using iOS 6.0.1 or iOS 6.0 in your iPhone 4, Redsn0w 0.9.15b3 tool supports to jailbreak. Windows users must run the Redsn0w file as an administrator. Mac users run it normally.
Step 01. Connect your iPhone 4 with the PC.
Step 03. Click on the “Extras” and then “Select IPSW” buttons.
Step 04. Select and open iPhone 4’s iOS in here. Recommend you to choose iOS 6.0, even if you are using iOS 6.0.1.
Step 05. Click on the jailbreak button.
Step 06. Put your iPhone 4 into DFU mode.
Unplug and switch off your iPhone 4.
Press and hold “Power” and “Home” buttons together for nearly 10 seconds.
Release only the “Power” button, keep holding “Home” button for another 15 seconds.
Step 07. It will prepare the jailberaking data. Check the Cydia install box and go next.
Step 08. There will be a message after rebooting your iPhone 4. Then go Back.
Step 09. You have completed the jailbreak process. Boot your iPhone as tethered. Put your iPhone 4 into DFU mode again. Follow the step 06 for it.
Step 10. Click on the Extras and then Just boot. After complete the boot, there will be a Cydia.