Changing timezone is very easy in Joomla. Please refer to the below steps to change timezone from Joomla admin panel.

1. Login to your Joomla admin panel. Make sure you login with administrator credentials.
   
   
2. Inside Global Configuration, click on the Server button.
   
   
3. At location settings, change the server time zone as per your requirement.
   
   

Note : There might be some extension on your website that can ignore this setting and this can lead to an inconsistent timezone display on your website. 

There are three workarounds to overcome this issue. 

1.Change timezone in .htaccess file

    You can add the below line in your .htaccess file to change the website timezone. 

        #Adjust default time zone 

        SetEnv TZ America/Washington

2. Change your server timezone.

If your website is running on shared hosting, your hosting provider may not change it for you as there will be several other clients of them hosting their website as well. However, you can surely change the vps or dedicated server timezone. 

3. Force the extension to use your choice of timezone

You can use the php function PHP function date_default_timezone_set and force the joomla extension to use your choice of timezone.