I have successfully resetted password on the Officeserv 7100 system, but sadly only way to do it is only how Samsung Expert TeddyB tells you.

For all future enthusiast:
Resetting system, neither switching to new OS files on Memory Card will reset the admin password, it will just update OS and password will remain the same. Former owner has probably changed the password to something sicko (like %%!IAmC00l0P_666) because OfficeServ Device Manager requires it to be changed first thing when you log in.

For all future owners of this cheap system:
It is too complicated for easy small-scale usage. Don't buy it from an auction for 150$ with 8 phones and all modules (like 2BRM/4DLM/4SLM) fitted. You expect something easy for money like this (150$), but this 2006 year 10000$ system is not it.