On your Secondary Navigation, which displays subpages on a page, you cannot individually remove links.
You can:
Unpublish the page that you do not want to display on the menu
Note: This will totally remove page access in the whole site.
Hide the page that you do not want to display on the menu
Note: This will hide the page, meaning the page is still published but is hidden and will not display in menus or the search. The only way a user could view a hidden page is to obtain a direct link from another user.
Note: Pages will still show in the Search and all other menus, but you can pick and choose which pages display on this individual page's secondary navigation.