Ecredit in 'MyDelta' - what can I do with it?

I have an Ecredit that shows up in my account for around $80 that I think is from an nonrefundable ticket I bought but never took last winter. Under 'terms' it says 'To redeem, you will need the Ticket Number' - do they mean the number from the ticket which resulted in the credit, or what?

Can I only use this to buy another ticket, or is it possible to use this kind of Ecredit toward other things like upgrading to a preferred seat or buying a skyclub pass or something?