I would recommend using their second suggestion, and placing the .htaccess file as described in that link in to your (renamed and) uploaded power gallery folder.
That should then enable smooth running of any gallery you create in the future on that remote site.
AddType x-mapp-php5 .php
Save the text file as .htaccess in the folder where you need to use PHP5 (or upload the file to the correct folder). The settings specified in the .htaccess file are recursive meaning that the settings will apply to the current folder where the file is saved as well as all subfolders.