Click on Upload/Download after you are done with the previous steps. You should see a Success notification when the upload is completed. Check the status of the sound under Existing sounds.Wait for several minutes, and press Save again if the status does not show Ready.
An example of a successfully uploaded sound
You can check for an available list of sounds with the -soundboard command. Then, play it with the -sb <sound name> command. Make sure that YAGPDB has the right permissions (i.e. connect to and speak in the voice channel).
You can delete sounds from the control panel. Look for the desired sound name under Existing sounds and press Delete to remove it from the list.