BP Social Theme customization

I’d like to make some change to the themes:

– change the Home Picture (the one with the “box head boy”:wink:

– change the footer (insert link and txt) 2009(c) Buddypress Theme in Action etc

– insert some link (hardcoded) in the headerbar. near “Visit”

– insert an image under the Welcome back “user”

Can you tell me the file I need to change?

There’s a way to proceed in order not to lose the changes in case of future template update?