You have to complete the NCVEC form 605 and on that form, there's a box to check if you want to change your callsign systematically. If checked, you will automatically be assigned a new callsign when your upgrade is processed by the FCC. So it kind of is automatic if you request it. Until then, you can use your current callsign/AE and operate with your new frequency privileges.
Also, you don't need to pass ANY exam in order to request a new systematically assigned callsign. You could submit form 605 to a VEC or submit the request online through the FCC license manager site.