Finally, my passport details got updated in VEVO. For those of you who need to update their passport details as well, here are the options:
1) You might be able to update your passport details online by logging into your ImmiAccount, opening your visa application, look for the 'Update us' link on the left navigation menu. If you click on that, it will give you a number of online forms that you can use. If the change of passport details form appears, you can use that one and submit online.
2) If however this option is not available for you, then you need to complete Form 929, attach a copy of your new passport and you can email to 929@border.gov.au.
In my case, option 1 is not working, so I just emailed my Form 929 together with a copy of my new and old passports. I am not sure though whether this is due to the fact that my visa application is already finalised.
Good luck!