Renaming file in directory

[eluser]Unknown[/eluser]
I have an image uploader that works well and stores the name of the file uploaded in a session. Once the files has been uploaded how do I then rename that file?

I would rename it during the uploaded but I need to rename it to an order number and I only get that order number after the image has been uploaded.

Thanks for any help.

[eluser]Jason Stanley[/eluser]
http://php.net/manual/en/function.rename.php