Log on as administrator?

Trying to clean up a computer I inherited, but am being limited as a
standard user.
Only options to select when logging on are admin (standard user) & qb
user (no one seems to remember the PW for!)
I've blanked the administrator PW with a reset disk, but there isn't a
switch user choice when at the log in screen!
How can I log on as actual administrator or change user called admin
to an actual administrator?