You should probably place all the handsets in their charging cradles before starting the update.

1. Log in to your DP750 base station using the web interface
   • The default credentials are admin / admin
2. Maintenance → Firmware Upgrade →
   1. Firmware Server Path → firmware.grandstream.com
   2. Handset Firmware Automatic Upgrade → Yes
3. Click Save and Apply
4. Reboot the base station

After the base reboots and upgrades to the latest version, the handsets will commence updating one at a time.

Be patient!