The best practice is to politely ask at check-in. Calling ahead of time is fruitless as any upgrades are entirely space-dependent and that's determined on the spot when you check in. From my experience, it's helpful to be proactive with this as the front desk will rarely hand over a complimentary upgrade on their own. All you have to say is "are there any complimentary upgrades available today?" At properties with upgraded rooms, I've been successful at getting an upgrade about 75% of the time.