3GS 3.0 to 4.1

[sunil355]

I have an iphone 3GS that was jailbroken by purple rain and is currently running 3.0.
I wish to upgrade to jailbroken 4.1.
Should I upgrade via itunes and then jailbreak using green poison or limerain.
What are the negatives of this method? What other methods can I use?
What is better to jailbreak with green poison or limerain?
I am not sure if i have any shsh files with cydia. How do I check this?

Thanks for your help

[Simon]

You can use tiny umbrella to check what SHSH you have. If you do not require a unlock then just update to 4.1 with itunes, then use greenpoison or limera1n to jailbreak.

[sunil355]

What if i wish to preserve the carrier unlock?

[Simon]

Then you either need to use the new pwnage tool or sn0wbreeze to create a custom 4.1 and restore to that.