For changing the time zone from the webmail please follow the below steps:
1.Login to webmail.
2.Then click on the settings option that is on the left side of the panel as shown in the below image.
3.Once you click on setting option you will get a new window as shown in the below image.
4.Now click on "User Interface" option that is highlighted in the above image.
5.Once you click on "User Interface" option you will get the below window as soon in the image below.
6.Now in the "Time zone" section just select on required option and then click on save option that is just below this window in yellow colour.
7.Once you save the setting your time zone will be changed to the above selected time zone.