Each experience has an options menu where you can either use to Delete files or Export them as IVZs.
Deleting experiences from the Project Library also deletes them from your hard drive. If you'd like to preserve files before deleting them, be sure to export them as IVZ files before hand.
Exporting IVZs allows you to share and save experiences to view at a later moment or for archival purposes. If you'd like to read more about this, start here.