I just got off a waitlist at my top choice school and i don’t know how to tell my original college that i will no longer be attending… do i call the admissions office?
Call or email.
Call as soon as possible! You canceling your spot at that school means someone else might be getting a spot at their dream college 
also, CONGRATULATIONS!!!
Do you have an online portal? You can also cancel there, but you don’t get a refund.