To prevent an additional system user from accessing the payroll click on the 'Client / Trader Manager' in the menu list, and select the 'Manage Assistant Administrator' option then further click on the blue button under Manage User which has Active account status. Further click on the 'Suspend Account' button. Enter the reason to suspend and finally enter your Passcode and click on 'Confirm' button.

The roadmap to remove the additional system user:
Roadmap:
Client / Trader Manager -> Manage Assistant Administrator -> Manage User (Active Account Status) -> Suspend Account -> Enter 4 digit Passcode -> Confirm.