Well, firstly, try not to fail anything. Even if you just barely pass, you're doing yourself a huge favour. I have no idea what Informatics is, but it's worth asking lots of questions or even getting a tutor to make sure that you understand enough to avoid failing the course.
When you try to transfer to a different course (and i think it if the transfer isn't internal, i.e.it's to another uni, you do have to apply through VTAC) they will look at your ENTER, but they'll mainly be concerned with your uni marks. Given that engineering is pretty far removed from arts/teaching they probably won't mind a great deal if your grades deviate from H1, in fact, a H3/P average would probably be sufficient.
I'm not sure if you'll be able to do a mid-year transfer or not, it's worth looking into. If you can't, you still have to put up with your course for the rest of the year. Although, I'd recommend that you do something artsy for your breadth subject if possible.
As for credit, you've done first year psych which will count, so will anything you do as arts breadth, but that'll probably be it, so you'll essentially be starting off as a first year again.
If it's just a matter of you trying to get used to a subject, stick with it until the end of the year and then reassess what you're dong. But, if you're unhappy in your degree and you were forced into it, you should definitely change! This isn't just about what you'll be learning over the next few years, it's potentially about your career as well. Nobody should get to have that much say over what you do (apart from you).