After uploading new files, I got this warning: Version 4.4.8 or greater is required. Use earlier versions at your own risk. Version 5.2 or greater is strongly recommended.

So I upgraded to PHP 5 through my hosting account. Yet the error persists.

Update: attempting to work through warnings. Where is php.ini?

Zenphoto reports the version number that your PHP provides. So if it is telling you it is 4.x.x, you did not successfully install or maybe select PHP 5.