On Dec 2 I am going YEG-YOW then on Dec 4th YOW-YYC-YEG.

I'm looking to burn a SSWU on both flights (it'll be the longest flight for the rest of the year that I do) and I have never used a SSWU before. Previously when I've upgraded on a latitude fare, I would upgrade at time of booking, but, now I understand I must wait until 4 days before the flight to try aerolotto?

Do I call 4 days before departure for both flights? Try online? What's the best strategy to ensure I'll be able to use these certs? Fare booking class is S if it helps.

Thanks!