Adding a Video Card

Hi

I don't know much about video cards and have a question about adding a second card. I bought an Aurora R5 in August that came with an I7-6700, 8Gb RAM, and a GeForce GTX 970 card with 4Gb RAM. I really need a better card for one of the games in particular that I play. I can't go out and buy a replacement card for 500-700 bucks. If I add a second 970, will I see any significant improvement in performance?

Thanks