Why do you believe that that Switch series has a system management Web Graphical User Interface?
As you understand it's not properly "just a common toy" to play with...that is a datacenter (expensive: refurbished or not) gear!
The manual you linked has this clear statement: "The switch supports login through the console port, telnet, SSH and NMS"
AFAIK no integrated web server to offer a Web GUI to Administrator(s): I'm afraid...these toys use CLI (Command Line Interface) only (with accessing methods listed above)!
The nearest thing I can think of is using something like H3C iMC (Web Based) to control the switch via SNMPv2...but it's really another story.