Hi Mike Squire,
It can't work. It doesn't work that way.
This excel document was uploaded by u to the server. When u downloaded, this excel is now on ur current computer. After u edit and save, this excel is still on ur current computer.
U cannot do a file save to save it into your server!!
What u can do is to use ftp to send this file to your server. This is the same thing that u do when u first upload it to the server.
Cheers