I hope you mean you put the CONTENTS of the upload folder there (if you are running your forum as root) as placing the Upload folder in root is a common mistake.
The PHP XML PECL is something that is done at the server level, either by your host or by you if running a VPS/Dedi.
You can find out if it's installed or not by going to yourdomain.com//admin.php?tools/phpinfo and look for something similar to this