upgrade from 3.0 jailbreak ?

[mphung]

I bought my iphone 3gs about 8 months ago and since then I have only jailbreak it on 3.0 firmware. I'm looking to upgrade and I am not sure where to begin. I have a Mac and PC. Any help will be appreciated. Thanks in advanced.

[hellodrsoul]

Most probably you can upgrade safely.you should know the following two things.
1.first check out your iphone's bootrom,if that is the older one(which should be on 3.0 and if you dont know how to check it,just google it and sorry i dont remember a direck link),than procede to step two.
2.use custom software from the following link,as this is the safest and easiest way to upgrade.
Download iPhone Custom Firmware 3.1.3 (IPSW) | iPhoneHeat

i have used these IPSWs to upgrade my 3gs and it surely works.sorry for my bad english as i am from Pakistan and hopefully you ll be able to understand.

[dhamien]

As you've had 3.0 installed, you definitely have the old bootrom meaning you can use a custom firmware.

As you also have a mac, I'd recommend you make the custom firmware yourself with pwnagetool.

You can find a guide here: iClarified - iPhone - How to Jailbreak Your iPhone 3GS Using PwnageTool [Mac]

When it asks you if you're already pwned, what it's really asking is if you're jailbroken and since you are, you should click 'yes'.