Change resolution possible from Launcher -> Settings or manually:
Open game client and open LauncherOption.if file with notepad and change settings ->
//DevModeIndex:
//0: 800x600 (4:3)
//1: 1024x768 (4:3)
//2: 1152x864 (4:3)
//3: 1280x720 (16:9)
//4: 1280x800 (16:10)
//5: 1280x960 (4:3)
//6: 1400x1050 (4:3)
//7: 1440x900 (16:10)
//8: 1600x90 (16:9)
//9: 1680x1050 (16:10)
//10: 1920x1080 (16:9)
WindowMode: 1 - On / 0 - Off
Save file.