The easiest way to change the timezone is via the Control Panel (Date and Time - change timezone). This changes the timezone and also changes your clock time  to compensate. Make sure to only change the timezone, the time will automatically be adjusted.

The data in RTC/Jazz takes timezone into account. You don't need to change any of the data in Jazz/RTC. From a client, you shouldn't notice that the server's timezone changed.

If you change the timezone of your client machine and view the history, the time will change by the difference between the old and new timezones. It's as if you took your computer and yourself and transported it to the new timezone. If I'm on the east coast and got a saw a WorkItem changed at 4:00 East and then transported myself and the machine to the west coat where the time was three hours earlier, the date should show up as 1:00 Pacific. One o'clock Pacific is the same time as Four o'clock Eastern.

If you change the timezone the RTC server is in, notification e-mail will still work as before.

Mail clients (e.g. Lotus Notes and Thunderbird) understand about timezones also. If you change the timezone of the client machine, the date attribute of the Lotus Notes mail will change in the same way that the RTC client date changed. Again it's as if the machine were transported to a new timezone.

WAS gets it timezone from the operating system, but you can also override the OS timezone it WAS.
See for details. https://jazz.net/forum/questions/76312/rtc-server-timezone-in-was