Most people prefer to play League of Legends in full screen to optimize performance, but there are certain times when you have to use the non-full screen. Doing so will make it easier for you to access windows and other programs while playing. This method can also improve performance slightly because sometimes switching from a game to the desktop will take a toll on CPU performance. Switching to a non-full window can be done very easily.
Step
Method 1 of 2: Switch to Not Full Screen While Playing
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Step 1. Start the game
Open the Settings window by pressing " Esc ".
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Step 2. Click the "Video" tab
Select "Windowed", not "Fullscreen" or "Borderless".
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Step 3. Continue playing
You can switch from full screen to non-full screen mode while playing using the Alt+Enter shortcut.
Method 2 of 2: Changing Configuration Files
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Step 1. Open the League of Legends folder on your computer
By default, the folder is in C:\Riot Games\League of Legends.
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Step 2. Open the "Configuration" folder
Open the Game.cfg file using Notepad.
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Step 3. Look for the words “Windowed=0”
Replace 0 with 1. Save the file.
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Step 4. Start the game
After you do this step, the game will run in a non-full screen. Set the screen resolution to make the window smaller.