Model C6900 - change password

> I would like to know how to change my Password (network key)

   You might try an oft-neglected resource:

      https://en.wikipedia.org/wiki/RTFM

   Visit http://netgear.com/support , put in your model number, and look
for Documentation.  Get the User Manual (at least).  Read.  Look for
"Types of Logins" and "Specify Basic WiFi Settings". Further reading
might not hurt, either.