File Upload

I was seeking if there is any module or how it could be done in drupal as follows, Can any one help?

We can easily upload files into a directory. But what i want, either i will select a file which are already uploaded, if not then go for upload a new one. Basically either you choose an already uploaded file or upload a new one.

If you choose a file from the dropdown list and at the same time upload a file, it will get the dropdown list file and discard the uploaded one.

Any ideas ?

Thanks in advance.