untheme-two-column….how to

I am using untheme-two-column.0.9 for my blog
and i would like to make some changes to it…..
i am new, and not sure whcile files to make changs
can anyone help, please? thanks!

1. I would liek to add a picture to the header. right now it is only showing blog name in grey background
2. change the backgound color of the navigation bar right below the header(where show my pages).. also add an expernal link to it
3. change background color of the sidebar