How do I know the Apple ID associated with a particular device (Macbook Pro)? How do I know the Apple ID associated with a particular device (Macbook Pro)? How do I change it?

One of my friend gifted me a Macbook Pro as a gift, and we don't know how to change its Apple ID. He has his Apple ID and password which works perfectly with this Macbook. After changing it, will updating to OS X 10.7 or reinstalling online possible?

Does this process completely disconnect from the previous Apple ID and connect with the new one?
System Preferences -> iCloud will tell you what Apple ID is currently being used on that computer and give you the option to sign out and change it if you wish. 

I'm unsure about the matters of updating ML. I think it will still work, but I can't say for sure.