3Com 4500 Getting Started Manual page 63

Default Users and Passwords 63
Use the admin default user name (no password) to login and carry out
initial Switch setup.
To set a password for the admin user in the CLI, enter the following from
system view:
[4500]local-user admin <cr>
[4500-luser-admin]password simple xxxxxxxx
(where xxxxxxxx is your chosen password).
Save the configuration in the User View.
For information on the lost password procedure please refer to the
Configuration Guide that is supplied with your Switch.