You cannot change system time in a VE because all VEes on the hardware node have the same system time.
To change the timezone using SSH directly on the VPS follow these guideliness
To set the timezone for GMT, add the following symbolic link:ln -sf /usr/share/zoneinfo/GMT /etc/localtime
Other way is to directly copy the proper timezone file and overwrite the /etc/localtime file
To set the timezone for GMT, run the following command:
cp /usr/share/zoneinfo/GMT /etc/localtime