You can change Time Zone of your webapplication by using “Central Admin” site.

1. Go to “Central Admin”
2. Click “Application management” from the quick launch.
3. Click “manage web applications” under “Web application” heading
4. Select web application on which you want to change the regional settings.
5. From the ribbon click “General setting” and select “General Settings” from the dropdown.
6. Setting modal dialog will appear, you can change the “default time zone” and other settings if you want to change, and click OK.  

 Do IIS reset to make sure that the changes are updated. You can also change regional settings on site level.