Where is get_post_meta value located?

You can do it either by editing the database table wp_postmeta: searching for the post_id = 63 and meta_key = ‘Header Info1’, and then editing the meta_value value.

The other, probably easier option, is to call a function update_post_meta(), like this:

<?php
query_posts("page_id=63");

while ( have_posts() ) : the_post();

    update_post_meta( get_the_ID(), 'Header Info1', 'new value' );

    echo get_post_meta( get_the_ID(), 'Header Info1', true ); 

endwhile; 
wp_reset_query();

Remember to remove that line after updating the meta field.

But doing this through code or editing the DB table probably beats the purpose of the using meta fields for additional dynamic post/page content.

Therefore, you might want to use some plugin which provides you with the GUI for editing the values of additional fields. Feel free to search for ‘wordpress custom meta fields plugin’, there are some great easy to use solutions.