The student's UPN is edited on the extended tab of the student profile. Here you may wish to move the UPN to Former UPN in order to keep as a record of any UPN change.
You are able enter a new UPN in its place, then save at the base of the tab.
If you wish to delete the UPN and are not ready to input a new one, you will need to go to Admin > Students > Group Updater.
Enter the student's Year Group and Form Group, then select UPN as Student Attribute.
Click Choose to view the student names in that Form.
Select the student you wish the delete the UPN for by placing a tick in the box, then Update at the base of the table.
If you had wished to change the student UPN, you could enter the new UPN value in the box, and then Update at the base to save this.
If the box is empty, it will overwrite the UPN with a blank box.
The UPN is removed, and you can confirm on the student's profile that the UPN has now gone.