This will remove the student record for good, there will be no way to retrieve the information after.

Step 1 - On the student record, go to Enrolment > Student Enrolment. Select Edit entry/exit.

Student must be set to "withdrawn" status 
Select the 'Remove completely' checkbox and Save:

PS: To be able to remove a student record, the user logged into the system needs to have permission. To set this permission, the SIS Admin on the school side needs to go Main Menu > Security > Accounts and select the account that will be able to delete student records and, under the PERMISSION tab: