You do have the ability to go standby for free as an Ascent - the gate agent may refer you to the Customer Service Center to do it, however. Definitely try to get to the earlier flight early enough to get your name on the list. You'll be ahead of everyone except Summits on the list.

I'm also an Ascent; I'm one for one on standby and even got a Stretch aisle seat.

You also might be able to upgrade the ticket to Classic Plus for less than $180, and as a Classic Plus ticket, you should be able to change your flight at no additional charge.