If you go to Admin > Personnel > Staff, search for the staff member's name (it will appear under Inactive Staff). On their profile, click on Change Passwords/Roles:
This takes you to this area on ScholarPack:
If you click on Delete SP Logon, this will clear the username and password for this user on ScholarPack. Deleting SP Logons is also useful if a staff member changes their name, as username's cannot be edited. A new Logon can then be created using their new name.