there are few of my friends who changed course last time. but only few of them got to change in the 1st semester and that was during middle of the semester while most of them got it in the 2nd semester. i guess ull have to stick with the course for a semester or so. u may try to contact the faculty first and see if theres anything they can do before u start the degree programme. here's the contact for the faculty economy :

Department of Economics
Faculty of Economics and Administration
Tel: +603-7967 3661 / 3749
Fax: +603-7956 7252
Email: tdid_fep@um.edu.my

and here's the contact for the faculty accounting :

Faculty of Business and Accountancy
Tel: +603-7967 3800
Fax: +603-7967 3810
Email: leechin@um.edu.my