1. You need to list your name on their system by calling Res desk
2. check-in at airport normally, if flt is ok they will give you a boarding pass instantly without seat# and let you pass through security/and or immigration, then exchange a new BP at the gate with seat#.
if the flt is full you will have to wait at the chk-in counter until last minute(45 mins bfr flight dept) if you are lucky to get on, then you have to rush to the gate
3. They Will Not upgrade you to Premium Y on nonrev, no exception very strict on that. They will u/g higher fare paid pax instead and let you seat at Economy, that's why exchange boarding pass at gate to have yr seat assignment.
4. It is a nice Airlines to fly with