Don’t ask me to buy a new phone. If I had money, I would have done that earlier! :)
my iphone to 2g is on iOS 4.2.1 im not sure if thats the verson or the iOS
OS is based perhaps on the chipset, if officially iPhone 2G can't be upgraded further up, then perhaps you can find modified OS on the net, then this is up to you if you want to go ahead and apply their modified custom firmware, do notice that this can put iphone end life.
Then don't ask how to perform an impossible upgrade!
The latest official firmware for the iPhone 2G is iOS 3.1.3.
I don't know if it's possible to get a newer hacked version on the 2G but considering that even the 3G is said to suffer in performance with iOS4 and the risks involved in such an update I don't think it's worth it.