Basic widget question

Well, I just reached a point that I don’t know anymore where to look for a solution, so I really hope anyone can give me some advice.

I’m having trouble customizing the Sidebar Widgets of my site.

My basic question is: when I add widgets to the sidebar, where is the list of these widgets, so I can customize them?

For example:

1. When I run the W3 Validator I get the following error:

Line 1428, column 64: document type does not allow element “li” here; missing one of “ul”, “ol”, “menu”, “dir” start-tag

<li id=”social-bookmarks” class=”widget widget_bookmarkwidget”><h2 class=”widgettitle”>Bookmarks</h2>

So I have to enclose the
<li> tag of the Bookmarks Widget. I’ve looked everwhere but I can’t find the code that I have to change. As far as I can see, it’s not in the didebar.php, not in the widgets.php and not in the functions.php

2. The same thing happens when I want to add a h2-title to my Currency Converter widget. I am searching over and over, but don’t know where to add to code…

Any suggestions, tips or answers are highly apreciated!!!

(I am running the widgets-ready Fjords01 theme. I have intermediate/good CSS-knowledge. Don’t know much about PHP yet – still learning.)