Go into the student record, and click on the side-tab Membership:
It will expand. Make sure you are on the Enrollment subtab. From there, you want to click Options > Registration > Change Student Status... Click Save.
It will show up on the Enrollment history as an S type of record, for a Status change.
E is for enrollment
W is for withdrawal
Y is for a YOG change
Fill in the necessary fields. If a student is going from Prereg to Active, it is important to note that the date should be the first day the student steps into the building to attend classes.