Getting user confirmation to replace file or not?

I am using easy upload add-on for uploading multiple files.It’s awesome for multiple file upload’s. I have a scenario of replacing the uploading files based on user confirmation.
I have modified the source code to easy-uploads addon to replace files.But I am not able to show a pop window to user for confirmation.I am stuck here.Please help me out with some suggestions.It would be really helpful for my further proceedings