With the project open in Podium, open the browser file panel, right-click the address bar and select ‘Go To Project Folder’. The file list now shows the contents of the project folder. There are pin icons at the left side next to each file that is still used in the project. You can then right-click sound files that are not pinned and use the ‘Delete’ command. Be careful though, because it is possible that you may have other projects that reference these unpinned files.