It's up to you but if you haven't studied for a while I'd start with the cert IV and go from there. I could have gone straight to Diploma but I decided to start at cert IV level as it's been a while since I studied plus I now have a 5 month old. Also there are TAFES out of Perth. I'm not sure where you are exactly but Google Great Southern Institute of Technology ( it seems none of them are actually called TAFE anymore and are institutes. Good luck with whatever you decide