Notes :
-I recommend redsn0w tethered users to backup + restore in itunes first before trying so you don't end up having to restore and delete everything if something goes wrong.
-3GS users with 06.15
-remember to backup anything first before trying anything
-any device with 4.2.1 will work
Download GreenPois0n RC5 here
For Windows users:
Mirror download:
For Mac users:
Mirror download: