The all the time zone files are stored in /usr/share/zoneinfo directory and its need to simlink to the /etc/localtime file to show the timezone as per your requirement.
Refer the following URL to set the timezone, for example, we are setting GMT timezone.
admin@root#ln -sf /usr/share/zoneinfo/GMT /etc/localtime
But make sure that you are logged into Server as root to execute the above command. Now check timezone has been changed or not?
admin@root # date
Tue Oct 7 03:49:53 GMT 2017