How do i update my course on UCAS

i had previously accepted an offer from my uni but decided to change my course, i still have the accepted offer on ucas but i have also been accepted into my new course. i want to open a student bank account but i cant as the course i was intially accepted into to is tied to my bank status code on ucas and the original course is only a year long, as opposed to a 3 year course which is the one i have changed to. i was wondering if i decline my place on ucas if the new course will appear or not.