For some reason one of my servers wouldn't allow me to change the timezone using the new GUI, not sure if this is a bug..

 To change the timezone is very simple and can be done several ways:

Powershell:

1. Start Powershell
2. Enter the following command:
   

   Get-Timezone -ListAvailable

   This will provide you a list with the available timezones, look up the one you want and take note of the ID
3. Enter the following command to change the timezone:
   

   Set-Timezone "<ID of Timezone>"

4. The timezone should be set now, you can check it in the GUI or by using 
   

   Get-Timezone

Server Manager

1. Start Server Manager 
2. Click on Local Server on the menu on the left hand side
3. In the list with server properties, click on Time zone. This brings you a dialog box showing the old style Adjust Time/Date. You should be able to change the time zone here