You can keep checking online and on the appropriate
thread in the General forum.
Meanwhile you can check Vodafone's Australia website, which lists Xperia M and the 4.3 update with Testing Scheduled, so keep checking every week until you get something: Vodafone Blog: Weekly Updates Wrap
You can also check XperiaBlog, they usually inform when an update is available. It was certified recently on PTCRB so it might take a little while for us to get it. XperiaBlog
We are all waiting, so next time make sure you check the above before posting *yet another where's my update thread*.