Sorry, I've been having some computer hardware problems here..
To remove the top nave menu entirely, edit the file named "directory"
Note this is a PHP file lacking the .php extension, so it it should be uploaded
and downloaded as ASCII/Text
Near line #114, simply comment out the include line for the top nav menu
//include("themes/$theme/navbar.top.php"

;
The bottom nav menu is included near line #144,
//include("themes/$theme/navbar.bottom.php"

;
To edit them, edit the navbar.top.php and navbar.bottom.php
files within the theme directory you are using,
/themes/original/navbar.bottom.php for example, if you use the original theme.
Always make a back-up copy of the file first