To find list of all available time zones, run:

[root@localhost ~]# timedatectl list-timezones

The syntax is as follows to set timezone and need to run as root user:

[root@localhost ~]# timedatectl set-timezone time_zone

In this example, set timezone to America/Chicago

[root@localhost ~]# timedatectl set-timezone America/Chicago

Verify new settings by typing the following two commands:

[root@localhost ~]# date
Sun Jun 18 15:25:03 CDT 2017
[root@localhost ~]# ls -l /etc/localtime 
lrwxrwxrwx 1 root root 37 Jun 18 15:24 /etc/localtime -> ../usr/share/zoneinfo/America/Chicago
[root@localhost ~]#

Change the TimeZone setting on /var/lib/pgsql/data/postgresql.conf to the value you want:

log_timezone = 'America/Chicago'
timezone = 'America/Chicago'

After that you need to restart the service:

[root@localhost ~]# systemctl restart postgresql