You can upload a file by selecting File->Upload..., clicking the Up Arrow icon on the toolbar, or by dragging the files onto Krio.
Krio allows you to download files from your MP3 player. To do this select File->Download... or click the Down Arrow on the menu bar.
To delete certain files from your MP3 player selected them from the list and select File->Delete or click the X icon on the toolbar.
File->Initialize will clear your MP3 player, deleting all the files.