Here's one I recommend. This one isn't complicated and easier to use for newer people.
To update game: You can press the triangle button on the Call of Duty game and Check for Update.
If you wan't to play online, Umm... I never played Call of Duty online multiplayer so I don't know how that works on CFW. So I won't be able to help you there.
But regular single player and local multiplayer should work fine.
Is "cos" "cousin"? Yes you can still Jailbreak his console even if he's been online before. You'll only get banned after you install CFW and connect to PSN. So your good to go. Even if they ban you, you can still jail break your PS3. Me for example, I connected online after I installed CFW and got banned but my Jailbreak still works fine for me. You'll have to take protective measures after you hack if you want to play online multiplayer and avoid getting banned.