If you notice that your fps is capped at 30 / 60 / or more fps, most likely Vsync is enabled, and it's capping your FPS in your monitor's refresh rate. Or you set an fps limit in-game or via external software. First, to unlock your FPS in LoL, try to turn Vsync off from in-game settings and your graphics card control panel. If this doesn't solve your issue, uncap the fps limit from the in-game settings or the external software you used to cap your fps.