My AE version is 7.6.4. I understand there is an update out, 7.7.2 (?), but I can find no download site, nor mention of it in App Store's Update section.
You should be able to update it from within the AirPort Utility app. If there is an update available for your unit, it will show up there.
Make sure you are connected to the Internet.
Open AirPort Utility. (Navigate to the /Applications/Utilities folder, to locate it.) AirPort Utility will display a badge to the right of the name of any AirPort base station in your network that has a firmware update available for it.
Select the AirPort base station you want to update.
let it run for awhile mine had the same problem and it appeared after awhile. login to your airport and look around and go back to the main page of the app.
My AE version is 7.6.4. I understand there is an update out, 7.7.2 (?), but I can find no download site, nor mention of it in App Store's Update section.
Once you get into the Utility, click on your Airport Extreme and you will see a box pop up. In the box if there is an update, it will show it and you will just click on it for the update
There are six generations of the AEBS. Check this out and figure out which one you have. Chances are you don't have the sixth one since you listed the wireless standard as 802.11n.
Mine was installed 1/2012, so it's a fifth generation device. Thanks for all the responses; I now have much more info than before and a higher level of comfort in terms of understanding the device.