Normally, the world-creation game "Minecraft" is displayed in windowed mode. This means that while the game is still visible on-screen, you don't get the game at its full-screen potential. It is possible to change the size, however, by using Windows' built-in, full-screen mode to let your "Minecraft" game take control of all you see on your computer monitor.
Click on the "Minecraft" screen to bring up the game.
Press "F11" on the keyboard to make the game full screen.
Press "F11" again to return the game to normal size, if desired.