You can download the class.upload.php as a package containing some demo scripts.
Package, with demo scripts and translation files
If you don't know which to get, download the zip file.
Available translations are so far: English, French, Spanish, Italian, Dutch, German, Czech, Swedish, Norwegian, Danish, Polish, Romanian, Croatian, Brazilian Portugese, Catalan, Turkish, Greek, Serbian, Ukrainian, Estonian, Slovak, Russian, Hebrew, Japanese, Indonesian, Vietnamese, Chinese and Traditional Chinese. Your language is not here? Contribute your translation! Note that the latest translations may not be included in the last release. Get them directly from the translation page.
Just the class, version text
You can get the class as a single text file here
You can get here previous versions, if you need to backport patches, etc...