This is a very hard route to upgrade and you often end up waitlisted and disappointed at the airport. The Sat night flights are near enough impossible in my experience. Weekday flights are a toss-up. Sat morning flights are easiest. Your best bet is to find a day that has R availability at booking (rare but not impossible)... also bear in mind there are a lot of 1Ks and Plats on these flights, so if you don't have that status, you are going to be way down on the waitlist... sorry to be the bearer of bad news!