Here is a link to get the AirPort firmware updates: [https://support.apple.com/en-us/HT201519|Update the software on your AirPort base station]
You'll need to first get the AirPort application which is located in your Utilities Folder running as well as have the AirPort Extreme connected to your modem and then your Mac connected to your AirPort all over Ethernet. Here's how it needs to be setup: [https://support.apple.com/kb/ph22796?locale=en_US|AirPort Utility: Set up a new base station]
You may need to try a new set of cables as that could be a problem too.