Check available timezones in your server by executing the command below.
Then simply delete the current timezone:
Create a symbolic link to /etc/localtime.
ln –s /usr/share/zoneinfo/Asia/Singapore /etc/localtime
If symblolic link not working, then you may use a copy command.
cp /usr/share/zoneinfo/Asia/Singapore /etc/localtime
yum install ntp
See all the timezones at this website http://www.pool.ntp.org/zone/asia. in the example below I will use Singapore timezone.
Also keep in mind that ntp only affects the system time. The hardware clock on your server will not reflect that. So you want to set it as well so that the correct time is maintained after reboot