Help with Modifying the Social Theme

Good Morning,

I have been getting familiar with the buddy press theme and I am running into a few roadblocks.
1. I tried to change the photo on the front page and the login fields disappeared. How do I change the photo and keep the rest of the header?
2. Also, while we are on this section, where do I change the verbiage next to the photo ("Welcome to BuddyPress Social, we connect you with your friend,….").
3. Is there a tutorial on how to customize the themes I should be viewing first?

Thank you for your help!