I have iphone 3g how do i update to higher ios?

Do i need to jailbreak it or can i update it and how? Which is best? I want to use viber and whatts app but the phone does not support due to old ios.

Plug ur phone into laptop or computer. Log into itunes. And then update to latest ios 6. I did it last week on my iphone 4.

4.2.1 is the highest and last firmware for the iphone 3g