jailbreak iOS 4.2.1 with Redsn0w

What you need:
iOS 4.2.1. firmware update
RedSn0w Mac 0.9.6b4 or 0.9.6b4 RedSn0w for Windows
iTunes with the latest update to 10.1.

Jailbreak
Upgrade your device with iTunes to firmware 4.2.1 just downloaded.
Connect your iPhone, iPod to your Mac or PC
Run the program
Once prompted, select the file. Firmware iOS of 4.2.1 that you used to upgrade your device.
Now select "Install Cydia "and click" Next. " Bring the device in DFU mode when the system will start and install the jailbreak.
When the program start in DFU follow the onscreen instructions and your device will be properly jailbreak in seconds.
Finished. In cases where you have a tethered jailbreak, Redsn0w will warn you.
The guide is very similar to earlier versions only makes a difference if you have a device to be unlocked in a tethered or untethered.

jailbreak iOS 4.2.1 with Redsn0w