Staff can be added/removed by logging into HelpAtSchools and then going to Admin->Manage Conferences:

Then, click on the Edit Staff tab:

To add a new staff member, scroll to the bottom and click Add a new staff member:

To delete staff, click on the red Delete button in the rightmost column:

Once you've finished, don't forget to scroll to the bottom and click Save:

Once the new staff member has been added, an account will be automatically created for them. 
They just need to go to HelpAtSchools and recover their password, following these steps: