Don't rename but replace exists file

Hi,

Currently CKFinder renames new file in case there is file with the same name. But I need to implement the following logic: during file upload if file with such name elready exists I'd like to prompt the user to replace the file or not.

For example: file img.jpg was uploaded previously, user tries to upload a new file with the same name (img.jpg).
CKFinder creates a new file img(1).jpg. But I want to create a confirmbox: "A file with the same name already exists. Do you want replace file?" And if user says yes, we should replace old img.jpg with new img.jpg.

I found a place where I can check if file already exists but I don't know how to create a Javascript prompt dialog. Right now I'm looking into
\ckfinder\core\connector\asp\CommandHandler\FileUpload.asp

Please advise.

Thanks