Image Header & Scroll Menu

Hi There

I actually change my wordpress.com to ww.wp.xz.cn and I love Leaf Theme for my new Blog ! I’m a real beginner here so it’s kinda hard to undertand codes …

http://edithstlaurentfitness.ca/

I can’t change the Header Image (full size of the screen)
I found some topic about header on support and try to do what everyone says but … I’m sure I do something wrong.

I also have problem with the scrolling menus … They are hidden by the Slider and can’t see other page uner the Menu …

Thank You !