wifi password change

> I need to change the password for my modem. [...]

   Why?  Which "the password"?

> Model: CM500|16x4 DOCSIS 3.0 Cable Modem

   Is that your "my modem"?

   A CM500 is a modem, not a (wireless) router, and, as a modem, it has
nothing to do with any "wifi password".

> [...] please, a simple answer.

   Please, a clear explanation of the problem which you are trying to
solve.

   Visit http://netgear.com/support , put in your model number, and look
for Documentation.  Get the User Manual.  Read.