depends, it your system set to the international time?, or is it set to your local time?
for local time: next time you reboot just go into the BIOS and change it .. or you can do it without reboot, read the wiki, its good your you
http://wiki.linuxquestions.org/wiki/Date
if your system is set to the international time, then its a problem with /etc/localtime with should be either a symlink or a file that contains data for your local time zone, the files are kept in /use/share/zoneinfo (note: they could be kept elsewhere, normally they are in the share directory) ... theres a program you could use to select the a time zone its "tzselect" ... just copy the correct file from the zoneinfo directory to /etc/localtime
