Q: I have airport extreme 6.0 and need to find my security key....any ideas?

I have a HP laptop I am trying to connect via wireless via my airport extreme router.  I need my security key to access the wirelss router and I don't know what that is.  I thought I might find my wirelss key via airport utility and when I go into Airport utility on my Mac Mini I get the following message. 

This version of AirPort Utility doesn't support this base station. Use AirPort Utility 5.6 to configure or manage this base station. AirPort Utility 5.6 is available at AirPort Service and Support.Clearly I have no idea what I am doing.  Any help is appreciated.