Help! Still on jailbroken IOS 3.0 on my 3g & need to upgrade

Hi, really hope someone can help. Over 2 years ago I successfully jailbroke and unlocked my iphone 3g with Redsn0w and Cydia so I could use my own sim in it. I used this really easy gizmondo step by step guide Jailbreak and Unlock iPhone 3.0

I'm a beginner to all this so found the guide really helpful. However ios 3.0 is now really old and incompatible with most apps. I want to move up to at least 3.1.2 but have no idea what I should do.

Can anyone offer or point me in the direction of a simple 'for dummies' style guide? Do I need to start from scratch?

The more I google the more confused I become as jailbreaking has really moved on since I originally did mine.

Thanks in advance

The iPhone 3G isn't so difficult to jailbreak/update.

As you have unlocked, you should try very hard to prevent your baseband from being updated. Yes... I know that ultrasn0w can unlock all iOS 3.x basebands but my experience is that the basebands that ship with 3.1.x are pretty bad news and you will get better stability from your current baseband.

Preventing baseband update is only possible with custom IPSW. This means pwnagetool 3.1.5 (mac) or sn0wbreeze ver ?? (windows). Also note that you should find the correct version of these apps (as the latest version probably doesn't have the ability to work with iOS 3.1.x IPSWs any more)

The regular contributors here at hackint0sh all have access to either a real mac or a hackint0sh mac so we have pretty much zero experience with sn0wbreeze. It's supposedly stable now, but older versions had some huge problems (so use at your own risk)

If you search around, you will find older posts that explain how to do what you want... You aren't the first person to ask this question.
You should not need to start from scratch. However you MUST sync your iPhone with iTunes before starting and allow iTunes to make a full backup (I usually zip up the backup, so I have a backup of the backup - just in case)

iOS 3.1.2 or 3.1.3 is a solid & stable OS for the iPhone 3G - many people have regretted updating their 3G iPhones to iOS 4.x

Closing thread.. duplicate/answered previously.