Note that the Airspace and Waypoint files will be uploaded to Soaring Spot automatically. Even better than that. They will be available in all file formats known to SeeYou. Automatically. You don't have to do anything but assign the files to the competition.
Often you will need to offer more files for download such as PDF files, various pictures and forms. You can do that by editing the rich edit text field in the "Additional downloads" section.
To delete the files which you have uploaded use the Explorer icon and edit the text accordingly.