You would probably need an actual hardware upgrade to really increase performance to a noticeable degree. Maybe you might see some performance increase if your GPU drivers were severely out of date, but for this particular game I doubt updating those would have a significant impact. If you do decide to upgrade a part of your system just keep in mind that a major video card upgrade may require a new power supply and may be bottlenecked if your cpu/mobo are not powerful enough to keep up with the video card upgrade you would be doing in this hypothetical situation.