zabbix-agent is already the newest version (3.4 -> 4.0)

[dannyhanes]

I am attempting to upgrade my Zabbix server from 3.4 to 4.0-2 and every time I run `sudo apt-get install --only-upgrade zabbix-server-mysql zabbix-frontend-php zabbix-agent` I just get

zabbix-server-mysql is already the newest version (1:3.4.14-1+xenial).
zabbix-agent is already the newest version (1:3.4.14-1+xenial).
zabbix-frontend-php is already the newest version (1:3.4.14-1+xenial).
0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.

I am following the instructions found here: https://www.zabbix.com/documentation.../debian_ubuntu

Any thoughts?