Randomise A Filename's Name

I've created an upload application that allows a user to upload a file a space on the web server.

What I want is when a user selects the file to upload, when the upload process takes places, a random number is generated and added to that filename.

I work out I can add the code:

intrandomnumber = Int((1000000-1+1)*Rnd+1)

but how do you do the change to the filename when it uploaded as I can change the filename name but the physical filename name would be the filename held on the user PC?