upgrading

I am about to upgrade to MarketPress from MP Lite, in order to get help here on 2 issues I have been having with Lite on this site that I am launching this week:
http://www.hickoryhillheather.com

I am worried that I could lose all my work customizing MP Lite.
What can I expect when I upgrade?

I have modified the icons.css as well as the marketpress.php