I am making a windows application. I used a generic template. Now i know where and how to change width and height but i want to have my applicatio be fullscreen or atleast windowed fullscreen.
Sadly, we are not interested in programming your application for you. You are asking how to do basic Win32 API stuff and getting the simplest, most straight-forward answers possible, but you haven't bothered to learn anything about the technology. If you had, you would be able to follow along.
So if you are going to do it, take some time to learn how to do it. Then ask questions.