editing checkout page

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https://www.mobileaudioheadquarters.com

I am running the smallbiz theme. I am trying to find out how to edit the checkout page to make it look more appealing. I have tried to follow this tutorial:
https://docs.getshopped.org/documentation/tutorial-wp-e-commerce-plugin-theme-customization/

but it doesnt seem to be working and I am a little confused because maybe I am not editing the correct file? I tried editing the wpsc-default.css as it says in the tutorial but it made no changes to the page. on a side note, i found that file if I open my site in ftp i can goto www/wpsc-theme and ALSO from main directory i can goto public_html/wpsc-theme . it seems that these two directories are the same and I thought maybe one was a shortcut so I added a file to the www folder and then opened public_html folder and it was not there. both folders however contain all of the same files inside as far as I can tell. is it supposed to be like this? So if anyone could help me out answering that questions and then getting me on the right track of making sure I am editing the correct file for the checkout page then possibly explain a little more how the code needs to be edited as that tutorial seems like it is missing a little explanation like when it says to add code on line 850, add to where? at the beginning or the end or the middle? I suppose a more proper way of explaining it would be to show the complete code after it has been edited? thanks alot for any help.