Biomedicine and Science at Melbourne are technically the same thing. I really don't see any reason why you'd want t transfer from Science to Biomed and risk losing some of your credits. Let's put it this way 'Biomedicine is basically Science for kids who want to do Medicine afterwards' - NOT because the course is harder or it's favoured by the admission committee of Med school but only because the course has been structured (with subjects and quota allocated accordingly) to make sure you have all the prerequisites for Medicine. the difficulties, if you chose the same/equivalent subjects as you would in Biomedicine, are the same. So my advice is, put the pride aside, and stay in Science. stay focused and do extremely well. get your prereqs done. and then nail whatever postgrad course you want to do. there's little to be gained, if any, from changing now.