The game already has low medium and high presets. Though as other have stated in previous threads your computer falls far below the minimum requirements for the alpha. Due to this FPS is going to suffer. As time progresses and as updates and optimizations are released the minimum requirements may be revised. At the moment unfortunately your only option is to deal with the lag or get a new rig, consider it an investment as im sure this game will offer entertainment for many years to come. Still playing RCT3 after all this time.