For the header image, you would want to find the image with this source that is contained in the header:
Then you would change the source to the image you want or just replace the logo.png with your own logo.png.
The colors of the PowerStore are controlled by the common.css, home.css.
To change the menu's color and styling you would either edit it using Menu Writer or modify the CSSMenuWriter/cssmw_home/menu.css
If you run into any issues with changing the styling, feel free to post a new thread or reply to this one.