Start with whatever template you are using and access it via ftp:
web >> assets >> templates >> layout# >> frame.html
web >> assets >> templates >> layout# >> css >> layout#_colors.css
These are the files you'll need to edit.
1.) You can change the background image of your website in the CSS file.
Code:
body{
background-image: url(image location);
}
2.) You can disable the mini-cart by commenting it out in the HTML file.
Code:
<!-- anything between brackets like this is commented out -->
If you try to
<!--
comment out a whole section, be aware that the comment will end
<!-- at the first "end comment" backet --->
and will leave the rest of the text exposed regardless
of there being another end bracket later
-->
Do a search on "HTML comments" and "CSS background-image" to learn more.