Page title, where to edit?

I think you're asking about the text you type into the field at the top of the page when you edit it or create a new one?

If that's the case, it's the text field right below the "Add New Page" heading when you're adding a new page :)

Hi, thanks for the replies :)
I meant the post title which could get longer than i want.
Looking for code that looks something like this:
<?php if (have_posts()) : while (have_posts()) : the_post(); ?>
And look for the post title but can't find it anywhere :/

Hi Erik,

You won't find your post title anywhere in the code - it's all handled from inside your WP Dashboard.

Yes, but going through every post to edit it manually will take ages :)
If i look at the twentyfifteen theme, the part i'm looking for is right there:
while ( have_posts() ) : the_post();

This is what i'm planning to do:"
http://www.doc4design.com/articles/wordpress-5ways-shorten-titles/

In that case, you may want to try this function:

add_filter( 'the_title', 'short_title' );
function short_title( $title ) { 
    $chars = 20; 
    if ( strlen( $title ) > $chars ) { 
        $title = substr( $title, 0, $chars ); 
        $title .= " …"; 
    } 
    return $title;
}

Adding PHP: https://generatepress.com/knowledgebase/adding-php-functions/