Customize theme

I am using theme 53307, are there any areas that I can NOT customize, I’m having trouble with the header area (I think it’s the header). My site is not live as I have chosen the wrong company to help me build my eCommerce 🙁

I am trying to learn on my own. Here is the test link.

http://184.154.188.35/~logotest/ya/gnar/wp-admin

Any help is greatly appreciated!