I have used this tool in the past and it works great
It is a executable and when run it looks for emacs and does some windows magic to make Emacs frames full screen. The readme has all the info you need to get it setup.
Just download the executable and add something like this to your config:
(defun toggle-full-screen ()
"Toggles full-screen mode for Emacs window on Win32."
(defun toggle-bars ()
"Toggles bars visibility."
(defun toggle-full-screen-and-bars ()
"Toggles full-screen mode and bars."
(global-set-key [f11] 'toggle-full-screen-and-bars)