How to hide a page in the main menù?

Hi guys,
I have a website from 9 months and now I would like to hide a page in the menù bar.
For example I have a menù composed by: home – who I am – Portfolio – Blog – Contact.
I would like to hide the page Portfolio. What do i have to do?

I have read on google that I have to find the tag ” wp_list_pages ” into the file functions. php.
Then seems that I have to insert the ID of the pages that I want to exclude.
A line like this (I don’t know if it’s right):

wp _list _pages(‘exclude=5,9,23 & title_li=< h2 >’ . __(‘Menu’) . ‘</ h2 >’ ); ?>

The problem is that I don’t find this tag.
Do you have any suggest on what to do?
I’ m using a child theme on minicorp.

Thank you very much.