best way to update a jailbroken 3gs 4.0 to 4.2.1 jailbroken on mac

[iSIILENT]

Hello,

Would like to know best way to update a jailbroken 3gs 4.0 with baseband 05.13.04, to 4.2.1 jailbreak as well. i would like to keep the ability to unlock in the future incase i tend to sell or something. also want to keep it so ill be able to update to 4.3 and jailbreak and keep it easy as well.

ill be using a mac

 

[noiceT]

Hello,

Would like to know best way to update a jailbroken 3gs 4.0 with baseband 05.13.04, to 4.2.1 jailbreak as well. i would like to keep the ability to unlock in the future incase i tend to sell or something. also want to keep it so ill be able to update to 4.3 and jailbreak and keep it easy as well.

ill be using a mac

Pwnage Tool:

http://blog.iphone-dev.org/

(see the first post)