Update Jailbroken Iphone?

I jailbroke my iPhone 4 (Verizon) under version 4.2.6 awhile back and want to update iPhone to 4.2.8. I used GreenPois0n to do it but I don't see anything for 4.2.8 on their website. I've never update my iPhone while is been Jailbroken before and wanted to make sure I do it right. Do I need to change from GreenPois0n to something else or do I just restore it through iTunes and rejailbreak it? Any help would be great thanks.