Hey, I was in a similar boat as you last year, I was doing Economics at Mac as a first year and now I'm doing Eco @ UNSW.
First I'm guessing you would need a high credit/D average (you're probably on track if you continue doing getting your current grades).
Then you look at the corresponding UNSW units:
http://credittransfer.unsw.edu.au/ . <-- Make sure you do units @ Mac which allows for a credit transfer to UNSW. Also, print out a form from somewhere on that link where you have to fill in what credits you think you may transfer.
At the end of the year (assuming u get a good average), you go to the Macquarie student centre across from the big food court, ask for an academic transcript (around $10?) and get it printed on the spot.
Apply for Comm from UAC, wait till you are approved (I got mine in the main round, like HSC -> Mac).
Go to UNSW's student central near the library, hand in your academic transcript along with a form you printed in the first step and you're done.
If you're not sure on what to do, they send you a brochure detailing the steps, you could also try to call student services and enrolment centre. Also, you will have a 0 WAM when you start UNSW.
