Upgrading Computer components

I have a question regarding what would be the most important update to my computer for optimal league of legends performance. I currently have a Intel Pentium CPU G3258 @ 3.20 Ghz and a Nivdia Geforce GTX 750 Ti. I currently only use this computer for league of legends and have no intentions of changing that in the future. In game, I get decently high fps ~144 capped, but occasionally it will start to jump down to as low as 60. I know thats still considered high fps but the constant jump from high to low causes the overall smoothness of the screen to be somewhat of a problem. Any advice is appreciated. Thanks!