Your user account comes set up with your default time zone. However, if you need to change this setting, you can do so through your profile.
Click your blue profile icon at the top right of the screen.
Select the top option on the drop-down menu.
Search for a time zone from the options.
Click on the white tick in the blue box to save.
Your new time zone should now be updated in our system. This means that, when viewing transactions, for example, you will see their timestamps in the local time that you selected: