UPGRAGE VIA WEB GUI
Open a web browser on PC and enter the IP address of the phone. Then, login with the administrator username and password. Go to Maintenance->Upgrade and Provisioning page, enter the IP address or the FQDN (firmware.grandstream.com) for the upgrade server in "Firmware Server Path" field and choose to upgrade via HTTP. Update the change by clicking the "Save and Apply" button. Then "Reboot" or power cycle the phone to update the new firmware.
When upgrading starts, the screen will show upgrading progress. When done you will see the phone restart again. Please do not interrupt or power cycle the phone when the upgrading process is on.
Firmware upgrading takes around 60 seconds in a controlled LAN or 5-10 minutes over the Internet. We recommend completing firmware upgrades in a controlled LAN environment whenever possible.
*** UPDATE ***
As of July 21, 2014, we have received a report from a partner that firmware version 188.8.131.52 has caused a problem with callparking in 3CX. This applies to GXP 2130/2140/2160.