Enter the IP address into a web browser and see what you can see. The admin user name is probably admin or administrator and the password is probably blank or password.
This product is a little older, so it may not look the same and this may not even work. But if it does, you'll probably see something similar to the information attached.
You'll need to enter the user codes into the printer, then go into Configuration/User Authentication and select what you want to manage.
Then as Art said, you'll need to enter the user code into the print driver. With the RPCS it is a one time thing and it's computer specific. With PCL, you can change the user code as you like.
Another note, you have to do something to initialize or tell the printer it has a hard drive, this is beyond me and usually our service department does this.