Instructions
Click on the Windows Start icon and select "Computer."
Find your "Ragnarok Online" program files. Their location will depend on where you chose to install them during the game client's installation. By default, program files are found on your computer's "C" drive.
Click on the "Setup" application file. This file is named "setup.exe" by default.
Customize your game client's monitor size by selecting a resolution from the drop down list and then pressing "OK."