Recently I needed to upgrade a VoIP phone Grandstream GXP-2000.
The procedure is quite simple if you have all required components.
Disclaimer: Guys, use this guide at your own risk. I can not guarantee that this guide will work for you. You will be responsible for the damages done to your phone. The main issue may arise only if you try using some weird firmware not compatible with your GXP-2000.
First of all, you need firmware for your Grandstream. Please keep in mind that some phones might have this version already. You can download pretty recent version here: Release_GXP2000-BT200_126.96.36.199.zip
Having installed TFTP Desktop, unzip firmware into the folder where you installed TFTP Desktop. Start TFTP Desktop Server. Please make sure that port UDP 69 on PC with TFTP Desktop is accessible from your local area network (you might need to configure firewall on your windows machine for that).
Now access your phone on http://IPaddressofthephone (default password: admin) and set IP address of TFTP server for updates to match the actual IP of the PC where TFTP Desktop is installed.
You have to make sure that the phone uses TFTP for updates not HTTP.
You can possibly set the update frequency 1 Day (for old version of the phone).
Then reboot the phone and monitor TFTP Desktop activity. You ll see how the phone requests various files and downloads them. Leave the phone for 5 minutes to complete updates (just to be sure). If the phone does not restart on its own reboot it manually. On the second boot the phone might perform another update by downloading a number of files from TFTP server (i.e. your PC). After the update, the phone shall reboot again. Then it comes online and you should get the phone with firmware updated.
It is a simple procedure and there should not be any issues if everything is done carefully.