How
Parent account?
Select student --> Access Account --> select account you want to remove --> delete
Admin account?
Select teacher/staff --> security setting --> teacher or admin tab --> uncheck the sign in --> submit
The way I do it is first take their access away under Staff Profile/Admin roles or account access and affiliations Then uncheck their access.
After that go in their demographics and unassign them under staff type (When I skipped this step they still showed as an option for teacher assigning) and uncheck the active box.