User Guide: http://www.grandstream.com/sites/default/files/Resources/DP750_DP720_User_Guide.pdf

Press and hold the Radio/Page button for 7 seconds until the Radio icon starts blinking Or in the web UI, press Subscribe icon.

Press Subscribe softkey, if available on the main screen, or access Menu → Registration → Register while the DP750 Radio icon is blinking

The Subscribe softkey appears only if DP720 is not registered to any DP750 base station.

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!