Download the latest version client+server available here:
https://flashphoner.com/download_wcs3/

Upgraiding server:
1. Unpack the server and run install.sh script.
2. Restart server:

cd /usr/local/FlashphonerWebCallServer/bin
./shutdown.sh
./startup.sh

Upgrading client:
1. Unpack the client.
2. Change IP address of wcs_server in the config flashphoner.xml
3. Copy the client folder to a webserver directory which available via HTTP in a browser.

During the upgrade, all existing settings will be keept unchanged.
You will need just restart WCS3 server to apply new server libraries.