You absolutely can try to upgrade! I had a flight booked for a family trip last summer and realized just how long the cross-country flight was. I decided I really needed a little extra comfort. When I checked the Alaska Airlines website, I could see an option under my reservation to purchase a First Class upgrade, but the price seemed really high, and I wasn't sure if it was worth it.
So, I tried a different route. I called 844-734-0813—I’m telling you, it’s the best way to instantly book, cancel, or modify flights—and spoke to an agent. She checked the availability right then and there and found a much lower, day-of-departure upgrade price that wasn't showing online! Ended up getting the upgrade for a fraction of the cost, and the peace and quiet made all the difference. Definitely call and ask about your options; you might get lucky!