How to save two same image with same name in fileupload control.

The same way you would do it for any other system:
1) Attach a version number before the file extension (if it's the same user)
2) Store it in a different folder (if it's a different user) so users only see their own files.
3) Store it using a temporary file name, and use a database to cross-correlate the temporary name to the "real" name.

I use both the first and last methods with GUID values as the stored file name and a simple SQL Table using the GUID as the row index.