[HELP] How to downgrade from 4.2.1 to 4.1 Baseband 06.16.00 [3GS]

[Ilyass]

Hello !!
Right now, i have iOS 4.2.1 Jailbroken and Unlocked with baseband updated 06.16.00, but the only problem is this jailbreak tethered, so i want to downgrade the iOS from 4.2.1 to 4.1 with untethered Jailbreak
btw i have SHSH saved
please, i really need a full tutorial how to do this!!!
Thanks in advance

 

[Ilyass]

Please HELPP!!!!

 

[PsstGreek]

The new just released GreenPois0n will untether your 3GS. No need to downgrade.