two basic ways;
- Drag and drop the file into the replay window you have open;
- The replay window has a black upward pointing arrow ( seventh from left side ), click on that, find the file using the browse option box and it will then be uploaded.
There is a file size limit and if SU will not allow the upload because it’s too big then use a file sharing site like Drop etc, upload file, copy URL location and post that herein so we can find it.