How to upgrade an iPhone 3G to ios 4.3?

Hi so I want to k ow if I can update a jailbroken iPhone 3G on ios 4.2.1 on baseband 06.15 and if it can be done can you give instructions

Ios 4.2.1 is the latest firmware for iphone 3g.so, there's no way to move into 4.3 offically. I have heard about whited00r but i personally not suggest you to use it allot of having problem with it