What you can do is this:
Put up.php in your active theme’s folder, and put this line at the top of your up.php file:
<?php /* Template Name: Up */ ?>
Create a page called Up in your WordPress Dashboard, then on the right side of the edit page screen, set the Template to ‘Up’.
Depending on what you are doing with this file, you may need to add more code to make it completely secure, but this should at least solve the problem of you being able to access/use that file.
Read the relevant WordPress Codex page for more information:
http://codex.wordpress.org/Pages#Creating_Your_Own_Page_Templates