Jerry,
I read through the Zabbix forum post you linked. Assuming the answer in the forum post is correct. It sounds like you would need to edit either /etc/zabbix/web/zabbix.conf.php or /etc/zabbix/zabbix_server.conf.
Here is what I would do:
1. cp /etc/zabbix/web/zabbix.conf.php /etc/zabbix/web/zabbix.conf.php.backup # make a backup
2 cp /etc/zabbix/zabbix_server.conf /etc/zabbix/zabbix_server.conf.backup # make a backup
3. less /etc/zabbix/web/zabbix.conf.php # Figure out which file you need to change
4. less /etc/zabbix/zabbix_server.conf # Figure out which file you need to change
5. nano /etc/zabbix/web/zabbix.conf.php OR nano /etc/zabbix/zabbix_server.conf # edit the file
If you are not familiar with using a text editor on the terminal you will probably want to follow a tutorial to get familiar with one prior to attempting step 5. In step 5 above I used the nano command. You can use whatever text editor you want(i.e. vim, nano emacs, etc). I personally use vim, but you can use whatever you want.
I hope that helps.