call 611 or go to a store; there is a fee. It was $15 a few years ago when I had to get my son's number changed.
Also you have to be the primary account holder or have those permissions to make the request.
Years ago I added a new line of service.... and several days later (without me even giving out my number to anyone) I started to receive about 10 calls a day from the "wrong number"... I complained to customer service and they changed my number (free of charge). They also saw that I had never changed my number before and that I was a loyal customer for many years ....
so if you are legitimately getting harassing calls.... They may change your number for free