the same way you kill anything.. smack the [censored] out of him until he is broken beat and scarred....
or failing that, drop the difficulty and get all hack and slash on his [censored]
The giant that we've seen looks friendly to me, so maybe we won't have to kill him at all! Dunno why I get that vibe from him... he looks some old wise thing that you can get help and advice from. Maybe you can befriend him with a quest or something.
sounds like hippie talk to me, if he's old wise thing than he will be easier to hack at.. hopefully
and you would be wrong not to do so, they put in something that looks challenging and dont wont you to challenge it, then it there fault when he dies.. i wanted to go mano-a-mano against mehrunes in OB