The login/logout links in the primary menu are set in functions.php

You can edit this section to change or remove the links

/*Add Login/Logout Menu Items*/
add_filter( 'wp_nav_menu_items', 'add_loginout_link', 10, 2 );
function add_loginout_link( $items, $args ) {
if (is_user_logged_in() && $args->theme_location == 'primary-menu') {
$items .= '<li><a href="'. wp_logout_url('my-account') .'">Logout</a></li>';
}
elseif (!is_user_logged_in() && $args->theme_location == 'primary-menu') {
$items .= '<li><a href="'. site_url('my-account') .'">Login</a></li>';
}
return $items;
}

The 'my-account' values are the slug of the page you wish the user to be redirected to on login/logout.