It took me forever to figure out a BF upgrade. It is not clearly explained on continental.com (CO, if you're listening, now it's two of us saying we didn't understand it!)

BF upgrades needs to be "paid for" via miles/co-pay. If it is open (R bucket availability) then you can have it at the point when you choose to pay. Choose your seat, enjoy the flight.

However, if it is not available you go onto a waitlist. Folks on the waitlist are prioritized by elite status and then the day/time they were added to the list. That waitlist expires at T-24 to departure, but everyone left on it goes to the airport list (the one you see at co.com) to be cleared by the airport. It's by elite status.

What makes it all clear-as-mud is that R comes and goes based on projected buying. It has little to do with the number of seats available and everything to do with how many seats they think they can sell. When/why/how is unknown to us, but there are clearly points prior to departure that the system runs some calculations and decides to release seats into R. If people are waitlisted they get the seats, if that is all clear then it shows up as mileage-deduct for fresh new bookings, and then if it stays available it eventually pops up in already-booked ressies as the elusive "upgrade this reservation with miles" link.

You can call to be put on the waitlist anytime prior to T-24, sooner the better. Cancellation or failure to clear gets your miles and money back.

I find doing it online when "upgrade with miles" appears in my ressie to be the easiest and least stressful way after the initial booking. If you're curious, search for your itin on Co.com as if it were a new booking and have it show award upgrade availability. If your itin is showing as allowing it for the segments you want you can call and be bumped right up despite the link not working in your online reservation.