Upgrading Grandstream devices via http/https/tftp can sometimes be difficult as there is no progress bar to monitor if the upgrade is actually taking place. Grandstream devices (depending on the model) can take a while to download the firmware before upgrading the device. Syslog is a great tool you can use to monitor this process.
Enable syslog on your device and send it to your syslog server:
Set firmware URL on your Grandstream device to your firmware server or Grandstream's firmware server (firmware.grandstream.com)
Reboot your device and then review the logs: