3GS iOS 3.1.2 upgrade to 4.0.1
My devise (3GS) is running on iOS 3.1.2 and I want to use 4.0.1 . I have some doubts for upgrading process jailbreak again.
I downloaded 4.0.1 ipsw file and I was going to restore it using iTunes , and then jailbreak using jailbreakme.com .
But I have doubts are -
1) SHSH file - how this will affect my process ,
do I need to create a shsh file ?
can I create a shsh file for 3.1.2 ?
2) Firmware - I assume latest firmware versions will be also upgraded while Im upgrading . Is there any advice to take.
Appreciate very much if I can get any idea regarding above OR any other way of upgrading from 3.1.2 to 4.0.1.