Nothing much you can do. If it only has 1 stick of RAM, then add a second stick of the same size (I assume it has a single stick of 4GB DDR3). With two RAM sticks the RAM will be operating at full speed rather than half speed. That could improve performance by around 10% - 15%.
Other than that there isn't anything to do to your laptop to improve game performance.
A SSD will not improve game performance unless the game is trying to load a lot of large graphic textures. It will only reduce lag assuming you are experiencing it while textures are being loaded into the game