I am new to Melia and have a question about the upgrade certificate. It says upgrade to a superior room upon availability, with online checkin, up to 48 hours in advance.

I will be at the Gran Melia Iguazu from Jan 2 to Jan 5, a very busy time no doubt. I was lucky that there was a recent price drop on those dates, but still pricey. Trying to decide whether to apply a 5% discount (worth $125 or so) or get the upgrade. If the upgrade goes through, that's worth more than $1000 on those nights (although I wouldn't pay that rate, it's worth more than $125 savings from the 5% - in a slow period the room is $100 more).

1) Does superior just mean better, or does it mean you can only upgrade to a "superior room" and not a "deluxe room"? This hotel doesn't show "superior rooms" they start at deluxe.
2) Is there capacity controls on the upgrade or if I see a one category upgrade (deluxe room jungle view to deluxe room falls view), it is available for the upgrade cert.
3) Is it confirmed upon on line check in or do I have to see whether it's still available when I arrive.
4) Is it straightforward to apply to the reservation? 48 hours ahead will be NYE and I think I won't be able to reach Melia customer service.