Under the message box, click the button that says "Go Advanced" it will bring you to another page that has even more options at the top. At the top of the message box on this new page, there will be a small paper clip button. Click that, and add the files from your computer into the new window that opens. After they are added, your replays should be attached. Hope that helped!
In other words, I'm leaving to my cottage tomorrow, and will stay until the weekend after. Don't have too much fun without me! Sorry for the inconvenience.