I use Bueno and there are two ways I know to do it:
Method 1 (preferred) — the CSS way
The Bueno theme comes with a custom.css file that you can edit that will supercece the style.css (and the style/color.css) definitions. This is good because you’re only changing the presentation of your blogs content. (As opposed to the actual content, -for which the developers at Woo Themes wrote the php to do.) If you ever update, back up the custom.css file and replace the new one with and your old one and your changes will be preserved.
So here’s how to hide the category navigation. Open custom.css in a text editor add:
/* Hide Category Navigation */
#navigation{ display:none; }
and save changes. You’re done!
Method 2 — Edit Theme’s PHP
The other way is to edit the theme’s Header.php file. (Which may be against Woo Theme’s usage restrictions for the free theme. I don’t know.)
Open Header.php in a text editor and delete the whole navigation div. You’ll have to do this again every time you upgrade.
Hope that helps. Cheers!