Lynx is a text-based browser on the server. It can't handle Zope and Plone manager frames.
The instructions intended that you use your regular browser (e.g., Firefox) from the machine on which you are running PuTTY after you have the PuTTY session running to the server (i.e., after you have logged on to the server through PuTTY, start Firefox on your Windows machine and enter the url indicated).
John