WN2500 - can't connect via Ethernet

I need to connect my desktop PC to my WN2500 via wired Ethernet to access the settings, and hopefully to access internet also.

The WN2500 is working ok as a range extender when set up using a wifi connection.  But when setting password for the extended wifi network, my browser tells me the connection is not secure and my data could be intercepted.  I want to enter the extender's settings using a wired connection and web browser interface for better security.  Also, I prefer to access the internet via the Ethernet ports. 

I am connected to the internet through my landlord's wifi router and do not have access to the router settings.  This is an application which I know is very common, but for some reason the extender manufacturers never discuss it in their marketing or support literature.

Thanks very much for any insights you can provide.