It depends on your status level. Diamond's and Plat's C+ upgrade window opens at time of purchase, Gold's opens at 3 days out, and Silver's opens at 24 hours (check-in time). What is your status level? There has to be C+ upgrade inventory however (not just an open seat). If you are a Diamond or Plat and purchasing a week or more advance, there will usually be C+ upgrade inventory and you are upgraded immediately. As mentioned above, the option to opt-out of a middle seat is only available at check-in time (the 24 hour mark). It is not available before then. If you are a Silver, you should just opt-out for now and opt-in at check-in time for window or aisle only.