With the Grandstream ATA on your network, you should be able to go to http://<ATAipaddress> in a browser. Mine is http://<ATAipaddress>:8080, but I can't remember if I changed it to that port or that was the default. The default password is 123. You can set it static, then in your router change the port rules to match the static.

You can also connect a PC or laptop to the LAN port of the ATA and it will hand out an IP. You can then access the web config by going to http://192.168.2.1.