Post Header and Navigation Menu

Hi, I am more than willing to admit that I am not a computer programmer as such, I have some pretty basic questions about your AMAZING theme (dying over the comments written in the code). Anyhow, my questions are:

1. How do I update the header image on the posts, I’ve poked around in the code, checked the forums can’t figure it out and would rather not mess everything up?
2. How do I add the navigation on the homepage across the main image again, again, poked around in the code and checked the forums?

I know these are basic, and you’re probably rolling your eyes as you read this but, I would appreciate your help!

Thanks!