How to Make PC Games Full Screenby Shea Laverty ; Updated September 22, 2017
Switching your game to full screen mode can offer you a better view of your game and minimize distractions during play. Full screen mode is supported by most games, so long as you know how to activate it. For some games, a simple keyboard shortcut is all that's needed, while others can be put into full screen mode through the game's menu.
Alt+Enter Keyboard Shortcut
For most games, you can press "Alt+Enter" on your keyboard to switch between full screen and windowed, making it possible to switch on the fly as needed. This shortcut also works for DOSBox, the DOS emulator used for many older games and some Steam releases. Some games use this shortcut for other functions, so if it doesn't work, check your game's documentation; switching to full screen mode may have just been given a different shortcut.
If your game doesn't use any shortcuts to switch to full screen mode, it's likely the game's settings menu will have the option. This option will most likely be found in the graphics or visuals menu, but may also be under general settings if neither of those menus are present.