Lead Developer
PHP is very unforgiving – it’s always a good idea to have access to your server via FTP or File Manager handy when changing it.
The functions.php file should never be changed – you can open this file using the file manager in your hosting control panel, and replace the contents of the file with the latest core file contents: https://themes.svn.wordpress.org/generatepress/1.3.39/functions.php
Hope this helps!