Well...that depends on your operating system...
If you're using Windows XP, there's a setting within Date and Time Properties, that will allow you to synchronize your system time with various servers.
Double-click the time on your System Tray to open this window.
Select the Internet Time tab.
Make sure the box is checked to Automatically synchronize with an Internet Time Server.
Select one of the servers using the drop down menu.
Click the Update Now button.
If the update fails using any of the servers available, there's a good chance your firewall protection is blocking the NTP port.
Simply open your firewall software and configure it to allow this port to connect for time synchronization.
I hope you found the above information useful...