If you want to switch degrees, find a list of all undergraduate programs available by faculty for Internal Program Transfer at UNSW.
www.student.unsw.edu.au
The link above describes how IPT (internal program transfer works). It goes into a lot of detail which I'll let you read in your free time, but essentially, for transferring into actuarial studies and commerce, you need one of the following:
1) WAM of 75 in MATH1131 and MATH1231
2) WAM of 75 in MATH1141 and MATH1241
3) Pass in MATH1151 and MATH1251 (having done both these myself, I can say they are very difficult, hence, only requiring a pass as compared to the other maths subjects)