Hi Samuel,
check the Codexfor more information about wp_nav_menu.
Normally you can use exclude=1,4,5 where the digitals are the page ids, not sure it will work, the codex doesn´t say a thing about it, but if you look into the wp_list_categories codex you will see what i mean.
@samuel Musarika
You can use following codex which can give you more knowledge about WP Nav Bar and Categories.
http://codex.wordpress.org/Good_Navigation_Links
http://codex.wordpress.org/Function_Reference/wp_nav_menu
Thanks