I am pretty sure you can only set your account timezone once. So if you have messed it up, you will have to contact Google support to modify it for you. Use the 'contact us' button from your account to do this.
You can't change it. If you really want to work with a different time zone: 1 - Create a new account 2 - activate this new account 3 - Request Google support team to migrate all your data from old account to new account (including Quality Score) Image ads and statistics data can not be migrated
This is new to me. I remember that it was impossible to change it some time ago. Anyway is good to know that is possible to change it now.
No - you cannot change the time zone yourself Yes - Google do have the ability to change it if you ask them - they did it for us