From Configure > Maintenance, Enable Automatic Upgrades and set the Maintenance Window Duration for 24 Hours.
This will initiate the upgrade procedure. The AP will:
1. Check into CloudTrax and see an update is available (5 min)
2. Download the update (10 min)
3. Tell CloudTrax its ready to update (5 min)
4. Install, reconfigure and check-in (5 min)
The whole process should be complete in ~20 minutes. After the process is complete, make sure to reset your Maintenance Window Duration to 2 or 3 hours.