Log into your server via SSH, here is a tutorial how you can do this
To check the time on your server use the command:
date
root@seedhost:~# date
Sa 23. Jun 12:48:37 CEST 2012
To update the date/time you need to use the command:
date -s
for example:
date -s 20:21:10
or
date -s 03/09/2012