If you have this router please be advised (as I was tonite from Netgear Support) that you MUST upgrade the firmware sequentially. In other words you cannot go from, say, 184.108.40.206 STRAIGHT TO the latest version, which is 220.127.116.11. Otherwise you will get a 'Page cannot be displayed' screen in the router interface when you try to do a firmware upload.
Netgear does not mention this on its website - so I thought I'd better to save everybody else the same bother I've had. As it happened I was able to upgrade from 18.104.22.168 to 22.214.171.124 THEN to the latest version. That might work for you. Otherwise - see above.
Meanwhile - COME ON NETGEAR GUYS. GET A GRIP FOR GOODNESS SAKE! THAT INFO SHOULD BE ON THE WEBSITE ON THE RELEVANT PRODUCT PAGE!!!