Game won't let me change Screen size, causing lag?

Game reset its Windowed Mode Size to 1600x900@60fps, and will NOT let me change it other than setting it to FullScreen Mode. BOTH settings are making the game lag uncontrollably where it's taking at least 10 seconds to move forward when I try to walk, and at least 20 seconds to open any of the menus? (I've restarted several times and am running a repair on it Via TapTap launcher but wondering if any other solution.) Game is completely unplayable for me.